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Posted to commits@lucene.apache.org by ho...@apache.org on 2018/05/21 15:23:10 UTC

[1/2] lucene-solr:master: SOLR-9480: A new 'relatedness()' aggregate function for JSON Faceting to enable building Semantic Knowledge Graphs

Repository: lucene-solr
Updated Branches:
  refs/heads/master 0c0fce3e9 -> 669b9e7a5


http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/cloud/TestCloudJSONFacetSKG.java
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diff --git a/solr/core/src/test/org/apache/solr/cloud/TestCloudJSONFacetSKG.java b/solr/core/src/test/org/apache/solr/cloud/TestCloudJSONFacetSKG.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.cloud;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.commons.lang.StringUtils;
+
+import org.apache.lucene.util.LuceneTestCase.Slow;
+import org.apache.lucene.util.TestUtil;
+import org.apache.solr.client.solrj.SolrClient;
+import org.apache.solr.client.solrj.SolrServerException;
+import org.apache.solr.client.solrj.embedded.JettySolrRunner;
+import org.apache.solr.client.solrj.impl.CloudSolrClient;
+import org.apache.solr.client.solrj.impl.HttpSolrClient;
+import org.apache.solr.client.solrj.request.CollectionAdminRequest;
+import org.apache.solr.client.solrj.request.QueryRequest;
+import org.apache.solr.client.solrj.response.QueryResponse;
+import org.apache.solr.common.SolrInputDocument;
+import org.apache.solr.common.params.SolrParams;
+import org.apache.solr.common.util.NamedList;
+import org.apache.solr.search.facet.FacetField;
+import static org.apache.solr.search.facet.RelatednessAgg.computeRelatedness;
+import static org.apache.solr.search.facet.RelatednessAgg.roundTo5Digits;
+
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/** 
+ * <p>
+ * A randomized test of nested facets using the <code>relatedness()</code> function, that asserts the 
+ * accuracy the results for all the buckets returned using verification queries of the (expected) 
+ * foreground &amp; background queries based on the nested facet terms.
+ * <p>
+ * Note that unlike normal facet "count" verification, using a high limit + overrequest isn't a substitute 
+ * for refinement in order to ensure accurate "skg" computation across shards.  For that reason, this 
+ * tests forces <code>refine: true</code> (unlike {@link TestCloudJSONFacetJoinDomain}) and specifices a 
+ * <code>domain: { 'query':'{!v=$back' }</code> for every facet, in order to garuntee that all popularity
+ * &amp; relatedness values returned can be proven with validation requests.
+ * </p>
+ * <p>
+ * (Refinement alone is not enough. Using the background query as the facet domain is neccessary to 
+ * prevent situations where a single shardX may return candidate bucket with no child-buckets due to 
+ * the normal facet intersections, but when refined on other shardY(s), can produce "high scoring" 
+ * SKG child-buckets, which would then be missing the foreground/background "size" contributions from 
+ * shardX.
+ * </p>
+ * 
+ * 
+ * 
+ * @see TestCloudJSONFacetJoinDomain
+ */
+@Slow
+public class TestCloudJSONFacetSKG extends SolrCloudTestCase {
+
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+  private static final String DEBUG_LABEL = MethodHandles.lookup().lookupClass().getName();
+  private static final String COLLECTION_NAME = DEBUG_LABEL + "_collection";
+
+  private static final int DEFAULT_LIMIT = FacetField.DEFAULT_FACET_LIMIT;
+  private static final int MAX_FIELD_NUM = 15;
+  private static final int UNIQUE_FIELD_VALS = 50;
+
+  /** Multivalued string field suffixes that can be randomized for testing diff facet/join code paths */
+  private static final String[] STR_FIELD_SUFFIXES = new String[] { "_ss", "_sds", "_sdsS" };
+  /** Multivalued int field suffixes that can be randomized for testing diff facet/join code paths */
+  private static final String[] INT_FIELD_SUFFIXES = new String[] { "_is", "_ids", "_idsS" };
+  
+  /** A basic client for operations at the cloud level, default collection will be set */
+  private static CloudSolrClient CLOUD_CLIENT;
+  /** One client per node */
+  private static ArrayList<HttpSolrClient> CLIENTS = new ArrayList<>(5);
+
+  @BeforeClass
+  private static void createMiniSolrCloudCluster() throws Exception {
+    // sanity check constants
+    assertTrue("bad test constants: some suffixes will never be tested",
+               (STR_FIELD_SUFFIXES.length < MAX_FIELD_NUM) && (INT_FIELD_SUFFIXES.length < MAX_FIELD_NUM));
+    
+    // we need DVs on point fields to compute stats & facets
+    if (Boolean.getBoolean(NUMERIC_POINTS_SYSPROP)) System.setProperty(NUMERIC_DOCVALUES_SYSPROP,"true");
+    
+    // multi replicas should not matter...
+    final int repFactor = usually() ? 1 : 2;
+    // ... but we definitely want to test multiple shards
+    final int numShards = TestUtil.nextInt(random(), 1, (usually() ? 2 :3));
+    final int numNodes = (numShards * repFactor);
+   
+    final String configName = DEBUG_LABEL + "_config-set";
+    final Path configDir = Paths.get(TEST_HOME(), "collection1", "conf");
+    
+    configureCluster(numNodes).addConfig(configName, configDir).configure();
+    
+    Map<String, String> collectionProperties = new LinkedHashMap<>();
+    collectionProperties.put("config", "solrconfig-tlog.xml");
+    collectionProperties.put("schema", "schema_latest.xml");
+    CollectionAdminRequest.createCollection(COLLECTION_NAME, configName, numShards, repFactor)
+        .setProperties(collectionProperties)
+        .process(cluster.getSolrClient());
+
+    CLOUD_CLIENT = cluster.getSolrClient();
+    CLOUD_CLIENT.setDefaultCollection(COLLECTION_NAME);
+
+    waitForRecoveriesToFinish(CLOUD_CLIENT);
+
+    for (JettySolrRunner jetty : cluster.getJettySolrRunners()) {
+      CLIENTS.add(getHttpSolrClient(jetty.getBaseUrl() + "/" + COLLECTION_NAME + "/"));
+    }
+
+    final int numDocs = atLeast(100);
+    for (int id = 0; id < numDocs; id++) {
+      SolrInputDocument doc = sdoc("id", ""+id);
+      for (int fieldNum = 0; fieldNum < MAX_FIELD_NUM; fieldNum++) {
+        // NOTE: some docs may have no value in a field
+        final int numValsThisDoc = TestUtil.nextInt(random(), 0, (usually() ? 5 : 10));
+        for (int v = 0; v < numValsThisDoc; v++) {
+          final String fieldValue = randFieldValue(fieldNum);
+          
+          // for each fieldNum, there are actaully two fields: one string, and one integer
+          doc.addField(field(STR_FIELD_SUFFIXES, fieldNum), fieldValue);
+          doc.addField(field(INT_FIELD_SUFFIXES, fieldNum), fieldValue);
+        }
+      }
+      CLOUD_CLIENT.add(doc);
+      if (random().nextInt(100) < 1) {
+        CLOUD_CLIENT.commit();  // commit 1% of the time to create new segments
+      }
+      if (random().nextInt(100) < 5) {
+        CLOUD_CLIENT.add(doc);  // duplicate the doc 5% of the time to create deleted docs
+      }
+    }
+    CLOUD_CLIENT.commit();
+  }
+
+  /**
+   * Given a (random) number, and a (static) array of possible suffixes returns a consistent field name that 
+   * uses that number and one of hte specified suffixes in it's name.
+   *
+   * @see #STR_FIELD_SUFFIXES
+   * @see #INT_FIELD_SUFFIXES
+   * @see #MAX_FIELD_NUM
+   * @see #randFieldValue
+   */
+  private static String field(final String[] suffixes, final int fieldNum) {
+    assert fieldNum < MAX_FIELD_NUM;
+    
+    final String suffix = suffixes[fieldNum % suffixes.length];
+    return "field_" + fieldNum + suffix;
+  }
+  private static String strfield(final int fieldNum) {
+    return field(STR_FIELD_SUFFIXES, fieldNum);
+  }
+  private static String intfield(final int fieldNum) {
+    return field(INT_FIELD_SUFFIXES, fieldNum);
+  }
+
+  /**
+   * Given a (random) field number, returns a random (integer based) value for that field.
+   * NOTE: The number of unique values in each field is constant acording to {@link #UNIQUE_FIELD_VALS}
+   * but the precise <em>range</em> of values will vary for each unique field number, such that cross field joins 
+   * will match fewer documents based on how far apart the field numbers are.
+   *
+   * @see #UNIQUE_FIELD_VALS
+   * @see #field
+   */
+  private static String randFieldValue(final int fieldNum) {
+    return "" + (fieldNum + TestUtil.nextInt(random(), 1, UNIQUE_FIELD_VALS));
+  }
+
+  
+  @AfterClass
+  private static void afterClass() throws Exception {
+    CLOUD_CLIENT.close(); CLOUD_CLIENT = null;
+    for (HttpSolrClient client : CLIENTS) {
+      client.close();
+    }
+    CLIENTS = null;
+  }
+  
+  /** 
+   * Test some small, hand crafted, but non-trivial queries that are
+   * easier to trace/debug then a pure random monstrosity.
+   * (ie: if something obvious gets broken, this test may fail faster and in a more obvious way then testRandom)
+   */
+  public void testBespoke() throws Exception {
+    { // trivial single level facet
+      Map<String,TermFacet> facets = new LinkedHashMap<>();
+      TermFacet top = new TermFacet(strfield(9), UNIQUE_FIELD_VALS, 0, null);
+      facets.put("top1", top);
+      final AtomicInteger maxBuckets = new AtomicInteger(UNIQUE_FIELD_VALS);
+      assertFacetSKGsAreCorrect(maxBuckets, facets, strfield(7)+":11", strfield(5)+":9", "*:*");
+      assertTrue("Didn't check a single bucket???", maxBuckets.get() < UNIQUE_FIELD_VALS);
+    }
+    
+    { // trivial single level facet w/sorting on skg
+      Map<String,TermFacet> facets = new LinkedHashMap<>();
+      TermFacet top = new TermFacet(strfield(9), UNIQUE_FIELD_VALS, 0, "skg desc");
+      facets.put("top2", top);
+      final AtomicInteger maxBuckets = new AtomicInteger(UNIQUE_FIELD_VALS);
+      assertFacetSKGsAreCorrect(maxBuckets, facets, strfield(7)+":11", strfield(5)+":9", "*:*");
+      assertTrue("Didn't check a single bucket???", maxBuckets.get() < UNIQUE_FIELD_VALS);
+    }
+
+    { // trivial single level facet w/ 2 diff ways to request "limit = (effectively) Infinite"
+      // to sanity check refinement of buckets missing from other shard in both cases
+      
+      // NOTE that these two queries & facets *should* effectively identical given that the
+      // very large limit value is big enough no shard will ever return that may terms,
+      // but the "limit=-1" case it actaully triggers slightly different code paths
+      // because it causes FacetField.returnsPartial() to be "true"
+      for (int limit : new int[] { 999999999, -1 }) {
+        Map<String,TermFacet> facets = new LinkedHashMap<>();
+        facets.put("top_facet_limit__" + limit, new TermFacet(strfield(9), limit, 0, "skg desc"));
+        final AtomicInteger maxBuckets = new AtomicInteger(UNIQUE_FIELD_VALS);
+        assertFacetSKGsAreCorrect(maxBuckets, facets, strfield(7)+":11", strfield(5)+":9", "*:*");
+        assertTrue("Didn't check a single bucket???", maxBuckets.get() < UNIQUE_FIELD_VALS);
+      }
+    }
+  }
+  
+  public void testRandom() throws Exception {
+
+    // since the "cost" of verifying the stats for each bucket is so high (see TODO in verifySKGResults())
+    // we put a safety valve in place on the maximum number of buckets that we are willing to verify
+    // across *all* the queries that we do.
+    // that way if the randomized queries we build all have relatively small facets, so be it, but if
+    // we get a really big one early on, we can test as much as possible, skip other iterations.
+    //
+    // (deeply nested facets may contain more buckets then the max, but we won't *check* all of them)
+    final int maxBucketsAllowed = atLeast(2000);
+    final AtomicInteger maxBucketsToCheck = new AtomicInteger(maxBucketsAllowed);
+    
+    final int numIters = atLeast(10);
+    for (int iter = 0; iter < numIters && 0 < maxBucketsToCheck.get(); iter++) {
+      
+      assertFacetSKGsAreCorrect(maxBucketsToCheck, TermFacet.buildRandomFacets(),
+                                buildRandomQuery(), buildRandomQuery(), buildRandomQuery());
+    }
+    assertTrue("Didn't check a single bucket???", maxBucketsToCheck.get() < maxBucketsAllowed);
+           
+
+  }
+
+  /**
+   * Generates a random query string across the randomized fields/values in the index
+   *
+   * @see #randFieldValue
+   * @see #field
+   */
+  private static String buildRandomQuery() {
+    if (0 == TestUtil.nextInt(random(), 0,10)) {
+      return "*:*";
+    }
+    final int numClauses = TestUtil.nextInt(random(), 3, 10);
+    final String[] clauses = new String[numClauses];
+    for (int c = 0; c < numClauses; c++) {
+      final int fieldNum = random().nextInt(MAX_FIELD_NUM);
+      // keep queries simple, just use str fields - not point of test
+      clauses[c] = strfield(fieldNum) + ":" + randFieldValue(fieldNum);
+    }
+    return buildORQuery(clauses);
+  }
+
+  private static String buildORQuery(String... clauses) {
+    assert 0 < clauses.length;
+    return "(" + StringUtils.join(clauses, " OR ") + ")";
+  }
+  
+  /**
+   * Given a set of term facets, and top level query strings, asserts that 
+   * the SKG stats for each facet term returned when executing that query with those foreground/background
+   * queries match the expected results of executing the equivilent queries in isolation.
+   *
+   * @see #verifySKGResults
+   */
+  private void assertFacetSKGsAreCorrect(final AtomicInteger maxBucketsToCheck,
+                                         Map<String,TermFacet> expected,
+                                         final String query,
+                                         final String foreQ,
+                                         final String backQ) throws SolrServerException, IOException {
+    final SolrParams baseParams = params("rows","0", "fore", foreQ, "back", backQ);
+    
+    final SolrParams facetParams = params("q", query,
+                                          "json.facet", ""+TermFacet.toJSONFacetParamValue(expected,null));
+    final SolrParams initParams = SolrParams.wrapAppended(facetParams, baseParams);
+    
+    log.info("Doing full run: {}", initParams);
+
+    QueryResponse rsp = null;
+    // JSON Facets not (currently) available from QueryResponse...
+    NamedList topNamedList = null;
+    try {
+      rsp = (new QueryRequest(initParams)).process(getRandClient(random()));
+      assertNotNull(initParams + " is null rsp?", rsp);
+      topNamedList = rsp.getResponse();
+      assertNotNull(initParams + " is null topNamedList?", topNamedList);
+    } catch (Exception e) {
+      throw new RuntimeException("init query failed: " + initParams + ": " + 
+                                 e.getMessage(), e);
+    }
+    try {
+      final NamedList facetResponse = (NamedList) topNamedList.get("facets");
+      assertNotNull("null facet results?", facetResponse);
+      assertEquals("numFound mismatch with top count?",
+                   rsp.getResults().getNumFound(), ((Number)facetResponse.get("count")).longValue());
+      if (0 == rsp.getResults().getNumFound()) {
+        // when the query matches nothing, we should expect no top level facets
+        expected = Collections.emptyMap();
+      }
+      assertFacetSKGsAreCorrect(maxBucketsToCheck, expected, baseParams, facetResponse);
+    } catch (AssertionError e) {
+      throw new AssertionError(initParams + " ===> " + topNamedList + " --> " + e.getMessage(), e);
+    } finally {
+      log.info("Ending full run"); 
+    }
+  }
+
+  /** 
+   * Recursive helper method that walks the actual facet response, comparing the SKG results to 
+   * the expected output based on the equivilent filters generated from the original TermFacet.
+   */
+  private void assertFacetSKGsAreCorrect(final AtomicInteger maxBucketsToCheck,
+                                         final Map<String,TermFacet> expected,
+                                         final SolrParams baseParams,
+                                         final NamedList actualFacetResponse) throws SolrServerException, IOException {
+
+    for (Map.Entry<String,TermFacet> entry : expected.entrySet()) {
+      final String facetKey = entry.getKey();
+      final TermFacet facet = entry.getValue();
+      final NamedList results = (NamedList) actualFacetResponse.get(facetKey);
+      assertNotNull(facetKey + " key missing from: " + actualFacetResponse, results);
+      final List<NamedList> buckets = (List<NamedList>) results.get("buckets");
+      assertNotNull(facetKey + " has null buckets: " + actualFacetResponse, buckets);
+
+      if (buckets.isEmpty()) {
+        // should only happen if the background query does not match any docs with field X
+        final long docsWithField = getNumFound(params("_trace", "noBuckets",
+                                                      "rows", "0",
+                                                      "q", facet.field+":[* TO *]",
+                                                      "fq", baseParams.get("back")));
+
+        assertEquals(facetKey + " has no buckets, but docs in background exist with field: " + facet.field,
+                     0, docsWithField);
+      }
+
+      // NOTE: it's important that we do this depth first -- not just because it's the easiest way to do it,
+      // but because it means that our maxBucketsToCheck will ensure we do a lot of deep sub-bucket checking,
+      // not just all the buckets of the top level(s) facet(s)
+      for (NamedList bucket : buckets) {
+        final String fieldVal = bucket.get("val").toString(); // int or stringified int
+
+        verifySKGResults(facetKey, facet, baseParams, fieldVal, bucket);
+        if (maxBucketsToCheck.decrementAndGet() <= 0) {
+          return;
+        }
+        
+        final SolrParams verifyParams = SolrParams.wrapAppended(baseParams,
+                                                                params("fq", facet.field + ":" + fieldVal));
+        
+        // recursively check subFacets
+        if (! facet.subFacets.isEmpty()) {
+          assertFacetSKGsAreCorrect(maxBucketsToCheck, facet.subFacets, verifyParams, bucket);
+        }
+      }
+    }
+  }
+
+  /**
+   * Verifies that the popularity &amp; relatedness values containined in a single SKG bucket 
+   * match the expected values based on the facet field &amp; bucket value, as well the existing 
+   * filterParams.
+   * 
+   * @see #assertFacetSKGsAreCorrect
+   */
+  private void verifySKGResults(String facetKey, TermFacet facet, SolrParams filterParams,
+                                String fieldVal, NamedList<Object> bucket)
+    throws SolrServerException, IOException {
+
+    final String bucketQ = facet.field+":"+fieldVal;
+    final NamedList<Object> skgBucket = (NamedList<Object>) bucket.get("skg");
+    assertNotNull(facetKey + "/bucket:" + bucket.toString(), skgBucket);
+
+    // TODO: make this more efficient?
+    // ideally we'd do a single query w/4 facet.queries, one for each count
+    // but formatting the queries is a pain, currently we leverage the accumulated fq's
+    final long fgSize = getNumFound(SolrParams.wrapAppended(params("_trace", "fgSize",
+                                                                   "rows","0",
+                                                                   "q","{!query v=$fore}"),
+                                                            filterParams));
+    final long bgSize = getNumFound(params("_trace", "bgSize",
+                                           "rows","0",
+                                           "q", filterParams.get("back")));
+    
+    final long fgCount = getNumFound(SolrParams.wrapAppended(params("_trace", "fgCount",
+                                                                   "rows","0",
+                                                                    "q","{!query v=$fore}",
+                                                                    "fq", bucketQ),
+                                                             filterParams));
+    final long bgCount = getNumFound(params("_trace", "bgCount",
+                                            "rows","0",
+                                            "q", bucketQ,
+                                            "fq", filterParams.get("back")));
+
+    assertEquals(facetKey + "/bucket:" + bucket + " => fgPop should be: " + fgCount + " / " + bgSize,
+                 roundTo5Digits((double) fgCount / bgSize),
+                 skgBucket.get("foreground_popularity"));
+    assertEquals(facetKey + "/bucket:" + bucket + " => bgPop should be: " + bgCount + " / " + bgSize,
+                 roundTo5Digits((double) bgCount / bgSize),
+                 skgBucket.get("background_popularity"));
+    assertEquals(facetKey + "/bucket:" + bucket + " => relatedness is wrong",
+                 roundTo5Digits(computeRelatedness(fgCount, fgSize, bgCount, bgSize)),
+                 skgBucket.get("relatedness"));
+    
+  }
+  
+  
+  /**
+   * Trivial data structure for modeling a simple terms facet that can be written out as a json.facet param.
+   *
+   * Doesn't do any string escaping or quoting, so don't use whitespace or reserved json characters
+   */
+  private static final class TermFacet {
+    public final String field;
+    public final Map<String,TermFacet> subFacets = new LinkedHashMap<>();
+    public final Integer limit; // may be null
+    public final Integer overrequest; // may be null
+    public final String sort; // may be null
+    /** Simplified constructor asks for limit = # unique vals */
+    public TermFacet(String field) {
+      this(field, UNIQUE_FIELD_VALS, 0, "skg desc"); 
+      
+    }
+    public TermFacet(String field, Integer limit, Integer overrequest, String sort) {
+      assert null != field;
+      this.field = field;
+      this.limit = limit;
+      this.overrequest = overrequest;
+      this.sort = sort;
+    }
+
+    /**
+     * recursively generates the <code>json.facet</code> param value to use for testing this facet
+     */
+    private CharSequence toJSONFacetParamValue() {
+      final String limitStr = (null == limit) ? "" : (", limit:" + limit);
+      final String overrequestStr = (null == overrequest) ? "" : (", overrequest:" + overrequest);
+      final String sortStr = (null == sort) ? "" : (", sort: '" + sort + "'");
+      final StringBuilder sb
+        = new StringBuilder("{ type:terms, field:" + field + limitStr + overrequestStr + sortStr);
+
+      // see class javadocs for why we always use refine:true & the query:$back domain for this test.
+      sb.append(", refine: true, domain: { query: '{!v=$back}' }, facet:");
+      sb.append(toJSONFacetParamValue(subFacets, "skg : 'relatedness($fore,$back)'"));
+      sb.append("}");
+      return sb;
+    }
+    
+    /**
+     * Given a set of (possibly nested) facets, generates a suitable <code>json.facet</code> param value to 
+     * use for testing them against in a solr request.
+     */
+    public static CharSequence toJSONFacetParamValue(final Map<String,TermFacet> facets,
+                                                     final String extraJson) {
+      assert null != facets;
+      if (0 == facets.size() && null == extraJson) {
+        return "";
+      }
+
+      StringBuilder sb = new StringBuilder("{ processEmpty: true, ");
+      for (String key : facets.keySet()) {
+        sb.append(key).append(" : ").append(facets.get(key).toJSONFacetParamValue());
+        sb.append(" ,");
+      }
+      if (null == extraJson) {
+        sb.setLength(sb.length() - 1);
+      } else {
+        sb.append(extraJson);
+      }
+      sb.append("}");
+      return sb;
+    }
+    
+    /**
+     * Factory method for generating some random facets.  
+     *
+     * For simplicity, each facet will have a unique key name.
+     */
+    public static Map<String,TermFacet> buildRandomFacets() {
+      // for simplicity, use a unique facet key regardless of depth - simplifies verification
+      // and le's us enforce a hard limit on the total number of facets in a request
+      AtomicInteger keyCounter = new AtomicInteger(0);
+      
+      final int maxDepth = TestUtil.nextInt(random(), 0, (usually() ? 2 : 3));
+      return buildRandomFacets(keyCounter, maxDepth);
+    }
+
+    /**
+     * picks a random value for the "sort" param, biased in favor of interesting test cases
+     *
+     * @return a sort string (w/direction), or null to specify nothing (trigger default behavior)
+     * @see #randomLimitParam
+     */
+    public static String randomSortParam(Random r) {
+
+      // IMPORTANT!!!
+      // if this method is modified to produce new sorts, make sure to update
+      // randomLimitParam to account for them if they are impacted by SOLR-12343
+      final String dir = random().nextBoolean() ? "asc" : "desc";
+      switch(r.nextInt(4)) {
+        case 0: return null;
+        case 1: return "count " + dir;
+        case 2: return "skg " + dir;
+        case 3: return "index " + dir;
+        default: throw new RuntimeException("Broken case statement");
+      }
+    }
+    /**
+     * picks a random value for the "limit" param, biased in favor of interesting test cases
+     *
+     * <p>
+     * <b>NOTE:</b> Due to SOLR-12343, we have to force an overrequest of "all" possible terms for 
+     * some sort values.
+     * </p>
+     *
+     * @return a number to specify in the request, or null to specify nothing (trigger default behavior)
+     * @see #UNIQUE_FIELD_VALS
+     * @see #randomSortParam
+     */
+    public static Integer randomLimitParam(Random r, final String sort) {
+      if (null != sort) {
+        if (sort.equals("count asc") || sort.startsWith("skg")) {
+          // of the known types of sorts produced, these are at risk of SOLR-12343
+          // so request (effectively) unlimited num buckets
+          return r.nextBoolean() ? UNIQUE_FIELD_VALS : -1;
+        }
+      }
+      final int limit = 1 + r.nextInt((int) (UNIQUE_FIELD_VALS * 1.5F));
+      if (limit >= UNIQUE_FIELD_VALS && r.nextBoolean()) {
+        return -1; // unlimited
+      } else if (limit == DEFAULT_LIMIT && r.nextBoolean()) { 
+        return null; // sometimes, don't specify limit if it's the default
+      }
+      return limit;
+    }
+    
+    /**
+     * picks a random value for the "overrequest" param, biased in favor of interesting test cases.
+     *
+     * @return a number to specify in the request, or null to specify nothing (trigger default behavior)
+     * @see #UNIQUE_FIELD_VALS
+     */
+    public static Integer randomOverrequestParam(Random r) {
+      switch(r.nextInt(10)) {
+        case 0:
+        case 1:
+        case 2:
+        case 3:
+          return 0; // 40% of the time, disable overrequest to better stress refinement
+        case 4:
+        case 5:
+          return r.nextInt(UNIQUE_FIELD_VALS); // 20% ask for less them what's needed
+        case 6:
+          return r.nextInt(Integer.MAX_VALUE); // 10%: completley random value, statisticaly more then enough
+        default: break;
+      }
+      // else.... either leave param unspecified (or redundently specify the -1 default)
+      return r.nextBoolean() ? null : -1;
+    }
+
+    /** 
+     * recursive helper method for building random facets
+     *
+     * @param keyCounter used to ensure every generated facet has a unique key name
+     * @param maxDepth max possible depth allowed for the recusion, a lower value may be used depending on how many facets are returned at the current level. 
+     */
+    private static Map<String,TermFacet> buildRandomFacets(AtomicInteger keyCounter, int maxDepth) {
+      final int numFacets = Math.max(1, TestUtil.nextInt(random(), -1, 3)); // 3/5th chance of being '1'
+      Map<String,TermFacet> results = new LinkedHashMap<>();
+      for (int i = 0; i < numFacets; i++) {
+        if (keyCounter.get() < 3) { // a hard limit on the total number of facets (regardless of depth) to reduce OOM risk
+          
+          final String sort = randomSortParam(random());
+          final Integer limit = randomLimitParam(random(), sort);
+          final Integer overrequest = randomOverrequestParam(random());
+          final TermFacet facet =  new TermFacet(field((random().nextBoolean()
+                                                        ? STR_FIELD_SUFFIXES : INT_FIELD_SUFFIXES),
+                                                       random().nextInt(MAX_FIELD_NUM)),
+                                                 limit, overrequest, sort);
+          results.put("facet_" + keyCounter.incrementAndGet(), facet);
+          if (0 < maxDepth) {
+            // if we're going wide, don't go deep
+            final int nextMaxDepth = Math.max(0, maxDepth - numFacets);
+            facet.subFacets.putAll(buildRandomFacets(keyCounter, TestUtil.nextInt(random(), 0, nextMaxDepth)));
+          }
+        }
+      }
+      return results;
+    }
+  }
+
+  /** 
+   * returns a random SolrClient -- either a CloudSolrClient, or an HttpSolrClient pointed 
+   * at a node in our cluster 
+   */
+  public static SolrClient getRandClient(Random rand) {
+    int numClients = CLIENTS.size();
+    int idx = TestUtil.nextInt(rand, 0, numClients);
+
+    return (idx == numClients) ? CLOUD_CLIENT : CLIENTS.get(idx);
+  }
+
+  /**
+   * Uses a random SolrClient to execture a request and returns only the numFound
+   * @see #getRandClient
+   */
+  public static long getNumFound(final SolrParams req) throws SolrServerException, IOException {
+    return getRandClient(random()).query(req).getResults().getNumFound();
+  }
+  
+  public static void waitForRecoveriesToFinish(CloudSolrClient client) throws Exception {
+    assert null != client.getDefaultCollection();
+    AbstractDistribZkTestBase.waitForRecoveriesToFinish(client.getDefaultCollection(),
+                                                        client.getZkStateReader(),
+                                                        true, true, 330);
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java
----------------------------------------------------------------------
diff --git a/solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java b/solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java
index d562076..84c34e1 100644
--- a/solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java
+++ b/solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java
@@ -1015,6 +1015,16 @@ public class QueryEqualityTest extends SolrTestCaseJ4 {
                      "currency(amount,USD)",
                      "currency('amount',USD)");
   }
+  public void testFuncRelatedness() throws Exception {
+    SolrQueryRequest req = req("fore","foo_s:front", "back","foo_s:back");
+    try {
+      assertFuncEquals(req,
+                       "agg_relatedness({!query v='foo_s:front'}, {!query v='foo_s:back'})", 
+                       "agg_relatedness($fore, $back)");
+    } finally {
+      req.close();
+    }
+  }
 
   public void testTestFuncs() throws Exception {
     assertFuncEquals("sleep(1,5)", "sleep(1,5)");

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/search/facet/DebugAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/test/org/apache/solr/search/facet/DebugAgg.java b/solr/core/src/test/org/apache/solr/search/facet/DebugAgg.java
index 8eed4c7..c7ce7c3 100644
--- a/solr/core/src/test/org/apache/solr/search/facet/DebugAgg.java
+++ b/solr/core/src/test/org/apache/solr/search/facet/DebugAgg.java
@@ -19,6 +19,7 @@ package org.apache.solr.search.facet;
 
 import java.io.IOException;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.queries.function.ValueSource;
@@ -88,8 +89,8 @@ public class DebugAgg extends AggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slot) throws IOException {
-      sub.collect(doc, slot);
+    public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
+      sub.collect(doc, slot, slotContext);
     }
 
     @Override
@@ -126,8 +127,8 @@ public class DebugAgg extends AggValueSource {
     }
 
     @Override
-    public int collect(DocSet docs, int slot) throws IOException {
-      return sub.collect(docs, slot);
+    public int collect(DocSet docs, int slot, IntFunction<SlotContext> slotContext) throws IOException {
+      return sub.collect(docs, slot, slotContext);
     }
 
     @Override

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/search/facet/DistributedFacetSimpleRefinementLongTailTest.java
----------------------------------------------------------------------
diff --git a/solr/core/src/test/org/apache/solr/search/facet/DistributedFacetSimpleRefinementLongTailTest.java b/solr/core/src/test/org/apache/solr/search/facet/DistributedFacetSimpleRefinementLongTailTest.java
index 0612755..ea3b5ef 100644
--- a/solr/core/src/test/org/apache/solr/search/facet/DistributedFacetSimpleRefinementLongTailTest.java
+++ b/solr/core/src/test/org/apache/solr/search/facet/DistributedFacetSimpleRefinementLongTailTest.java
@@ -373,7 +373,10 @@ public class DistributedFacetSimpleRefinementLongTailTest extends BaseDistribute
     NamedList<NamedList> all_facets = (NamedList) queryServer
       ( params( "q", "*:*", "shards", getShardsString(), "rows" , "0", "json.facet",
                 "{ foo : { " + commonJson + " field: foo_s, facet: { " +
-                ALL_STATS_JSON + " bar: { " + commonJson + " field: bar_s, facet: { " + ALL_STATS_JSON + "} } } } }"
+                ALL_STATS_JSON + " bar: { " + commonJson + " field: bar_s, facet: { " + ALL_STATS_JSON +
+                // under bar, in addition to "ALL" simple stats, we also ask for skg...
+                ", skg : 'relatedness($skg_fore,$skg_back)' } } } } }",
+                "skg_fore", STAT_FIELD+":[0 TO 40]", "skg_back", STAT_FIELD+":[-10000 TO 10000]"
       ) ).getResponse().get("facets");
     
     assertNotNull(all_facets);
@@ -411,7 +414,7 @@ public class DistributedFacetSimpleRefinementLongTailTest extends BaseDistribute
     List<NamedList> tail_bar_buckets = (List) ((NamedList)tail_Bucket.get("bar")).get("buckets");
    
     NamedList tailB_Bucket = tail_bar_buckets.get(0);
-    assertEquals(ALL_STATS.size() + 2, tailB_Bucket.size()); // val,count ... NO SUB FACETS
+    assertEquals(ALL_STATS.size() + 3, tailB_Bucket.size()); // val,count,skg ... NO SUB FACETS
     assertEquals("tailB", tailB_Bucket.get("val"));
     assertEquals(17L, tailB_Bucket.get("count"));
     assertEquals(35L, tailB_Bucket.get("min"));
@@ -423,6 +426,18 @@ public class DistributedFacetSimpleRefinementLongTailTest extends BaseDistribute
     assertEquals(16910.0D, (double) tailB_Bucket.get("sumsq"), 0.1E-7);
     // assertEquals(1.78376517D, (double) tailB_Bucket.get("stddev"), 0.1E-7); // TODO: SOLR-11725
     assertEquals(1.70782513D, (double) tailB_Bucket.get("stddev"), 0.1E-7); // json.facet is using the "uncorrected stddev"
+
+    // check the SKG stats on our tailB bucket
+    NamedList tailB_skg = (NamedList) tailB_Bucket.get("skg");
+    assertEquals(tailB_skg.toString(),
+                 3, tailB_skg.size()); 
+    assertEquals(0.19990D,    tailB_skg.get("relatedness"));
+    assertEquals(0.00334D,    tailB_skg.get("foreground_popularity"));
+    assertEquals(0.00334D,    tailB_skg.get("background_popularity"));
+    //assertEquals(12L,       tailB_skg.get("foreground_count"));
+    //assertEquals(82L,       tailB_skg.get("foreground_size"));
+    //assertEquals(12L,       tailB_skg.get("background_count"));
+    //assertEquals(3591L,     tailB_skg.get("background_size"));
   }
 
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacetRefinement.java
----------------------------------------------------------------------
diff --git a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacetRefinement.java b/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacetRefinement.java
index 1e62cb2..687adde 100644
--- a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacetRefinement.java
+++ b/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacetRefinement.java
@@ -407,6 +407,75 @@ public class TestJsonFacetRefinement extends SolrTestCaseHS {
               "}"
       );
 
+      // test that SKG stat reflects merged refinement
+      client.testJQ(params(p, "rows", "0", "q", "*:*", "fore", "${xy_s}:X", "back", "${num_d}:[0 TO 100]",
+                           "json.facet", "{"
+                           + "   cat0:{ ${terms} type:terms, field: ${cat_s}, "
+                           + "          sort:'count desc', limit:1, overrequest:0, refine:true, "
+                           + "          facet:{ s:'relatedness($fore,$back)'} } }")
+                    , "facets=={ count:8, cat0:{ buckets:[ "
+                    + "   { val:A, count:4, "
+                    + "     s : { relatedness: 0.00496, "
+                    //+ "           foreground_count: 3, "
+                    //+ "           foreground_size: 5, "
+                    //+ "           background_count: 2, "
+                    //+ "           background_size: 4, "
+                    + "           foreground_popularity: 0.75, "
+                    + "           background_popularity: 0.5, "
+                    + "         } } ] }" +
+                    "}"
+                    );
+      
+      // SKG under nested facet where some terms only exist on one shard
+      { 
+        // sub-bucket order should change as sort direction changes
+        final String jsonFacet = ""
+          + "{ processEmpty:true, "
+          + " cat0:{ ${terms} type:terms, field: ${cat_s}, "
+          + "        sort:'count desc', limit:1, overrequest:0, refine:true, "
+          + "        facet:{ processEmpty:true, "
+          + "                qw1: { ${terms} type:terms, field: ${qw_s}, mincount:0, "
+          + "                       sort:'${skg_sort}', limit:100, overrequest:0, refine:true, "
+          + "                       facet:{ processEmpty:true, skg:'relatedness($fore,$back)' } } } } }";
+        final String bucketQ = ""
+          + "             { val:Q, count:1, "
+          + "               skg : { relatedness: 1.0, "
+          + "                       foreground_popularity: 0.25, "
+          + "                       background_popularity: 0.0, "
+          // + "                       foreground_count: 1, "
+          // + "                       foreground_size: 3, "
+          // + "                       background_count: 0, "
+          // + "                       background_size: 4, "
+          + "               } },";
+        final String bucketW = ""
+          + "             { val:W, count:1, "
+          + "               skg : { relatedness: 0.0037, "
+          + "                       foreground_popularity: 0.25, "
+          + "                       background_popularity: 0.25, "
+          // + "                       foreground_count: 1, "
+          // + "                       foreground_size: 3, "
+          // + "                       background_count: 1, "
+          // + "                       background_size: 4, "
+          + "               } },";
+        
+        client.testJQ(params(p, "rows", "0", "q", "*:*", "fore", "${xy_s}:X", "back", "${num_d}:[0 TO 100]",
+                             "skg_sort", "skg desc", "json.facet", jsonFacet)
+                      , "facets=={ count:8, cat0:{ buckets:[ "
+                      + "   { val:A, count:4, "
+                      + "     qw1 : { buckets:["
+                      + bucketQ
+                      + bucketW
+                      + "  ] } } ] } }");
+        client.testJQ(params(p, "rows", "0", "q", "*:*", "fore", "${xy_s}:X", "back", "${num_d}:[0 TO 100]",
+                             "skg_sort", "skg asc", "json.facet", jsonFacet)
+                      , "facets=={ count:8, cat0:{ buckets:[ "
+                      + "   { val:A, count:4, "
+                      + "     qw1 : { buckets:["
+                      + bucketW
+                      + bucketQ
+                      + "  ] } } ] } }");
+      }
+    
       // test partial buckets (field facet within field facet)
       client.testJQ(params(p, "q", "*:*",
           "json.facet", "{" +

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacets.java
----------------------------------------------------------------------
diff --git a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacets.java b/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacets.java
index b6afdb8..4402d78 100644
--- a/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacets.java
+++ b/solr/core/src/test/org/apache/solr/search/facet/TestJsonFacets.java
@@ -213,6 +213,245 @@ public class TestJsonFacets extends SolrTestCaseHS {
   }
 
   @Test
+  public void testExplicitQueryDomain() throws Exception {
+    Client client = Client.localClient();
+    indexSimple(client);
+
+    { // simple 'query' domain
+      
+      // the facet buckets for all of the requests below should be identical
+      // only the numFound & top level facet count should differ
+      final String expectedFacets
+        = "facets/w=={ buckets:["
+        + "  { val:'NJ', count:2}, "
+        + "  { val:'NY', count:1} ] }";
+      
+      assertJQ(req("rows", "0", "q", "cat_s:B", "json.facet",
+                   "{w: {type:terms, field:'where_s'}}"),
+               "response/numFound==3",
+               "facets/count==3",
+               expectedFacets);
+      assertJQ(req("rows", "0", "q", "id:3", "json.facet",
+                   "{w: {type:terms, field:'where_s', domain: { query:'cat_s:B' }}}"),
+               "response/numFound==1",
+               "facets/count==1",
+               expectedFacets);
+      assertJQ(req("rows", "0", "q", "*:*", "fq", "-*:*", "json.facet",
+                   "{w: {type:terms, field:'where_s', domain: { query:'cat_s:B' }}}"),
+               "response/numFound==0",
+               "facets/count==0",
+               expectedFacets);
+      assertJQ(req("rows", "0", "q", "*:*", "fq", "-*:*", "domain_q", "cat_s:B", "json.facet",
+                   "{w: {type:terms, field:'where_s', domain: { query:{param:domain_q} }}}"),
+               "response/numFound==0",
+               "facets/count==0",
+               expectedFacets);
+    }
+    
+    { // a nested explicit query domain
+
+      // for all of the "top" buckets, the subfacet should have identical sub-buckets
+      final String expectedSubBuckets = "{ buckets:[ { val:'B', count:3}, { val:'A', count:2} ] }";
+      assertJQ(req("rows", "0", "q", "num_i:[0 TO *]", "json.facet",
+                   "{w: {type:terms, field:'where_s', " + 
+                   "     facet: { c: { type:terms, field:'cat_s', domain: { query:'*:*' }}}}}")
+               , "facets/w=={ buckets:["
+               + "  { val:'NJ', count:2, c: " + expectedSubBuckets + "}, "
+               + "  { val:'NY', count:1, c: " + expectedSubBuckets + "} "
+               + "] }"
+               );
+    }
+
+    { // an (effectively) empty query should produce an error
+      ignoreException("'query' domain can not be null");
+      ignoreException("'query' domain must not evaluate to an empty list");
+      for (String raw : Arrays.asList("null", "[ ]", "{param:bogus}")) {
+        expectThrows(SolrException.class, () -> {
+            assertJQ(req("rows", "0", "q", "num_i:[0 TO *]", "json.facet",
+                         "{w: {type:terms, field:'where_s', " + 
+                         "     facet: { c: { type:terms, field:'cat_s', domain: { query: "+raw+" }}}}}"));
+          });
+      }
+    }
+  }
+
+  
+  @Test
+  public void testSimpleSKG() throws Exception {
+    Client client = Client.localClient();
+    indexSimple(client);
+
+    // using relatedness() as a top level stat, not nested under any facet
+    // (not particularly useful, but shouldn't error either)
+    assertJQ(req("q", "cat_s:[* TO *]", "rows", "0",
+                 "fore", "where_s:NY", "back", "*:*",
+                 "json.facet", " { skg: 'relatedness($fore,$back)' }")
+             , "facets=={"
+             + "   count:5, "
+             + "   skg : { relatedness: 0.00699,"
+             + "           foreground_popularity: 0.33333,"
+             + "           background_popularity: 0.83333,"
+             + "   } }"
+             );
+    
+    // simple single level facet w/skg stat & sorting
+    for (String sort : Arrays.asList("index asc", "skg desc")) {
+      // the relatedness score of each of our cat_s values is (conviniently) also alphabetical order
+      // so both of these sort options should produce identical output
+      // and testinging "index" sort allows the randomized use of "stream" processor as default to be tested
+      assertJQ(req("q", "cat_s:[* TO *]", "rows", "0",
+                   "fore", "where_s:NY", "back", "*:*",
+                   "json.facet", ""
+                   + "{x: { type: terms, field: 'cat_s', sort: '"+sort+"', "
+                   + "      facet: { skg: 'relatedness($fore,$back)' } } }")
+               , "facets=={count:5, x:{ buckets:["
+               + "   { val:'A', count:2, "
+               + "     skg : { relatedness: 0.00554, "
+               //+ "             foreground_count: 1, "
+               //+ "             foreground_size: 2, "
+               //+ "             background_count: 2, "
+               //+ "             background_size: 6,"
+               + "             foreground_popularity: 0.16667,"
+               + "             background_popularity: 0.33333, },"
+               + "   }, "
+               + "   { val:'B', count:3, "
+               + "     skg : { relatedness: 0.0, " // perfectly average and uncorrolated
+               //+ "             foreground_count: 1, "
+               //+ "             foreground_size: 2, "
+               //+ "             background_count: 3, "
+               //+ "             background_size: 6,"
+               + "             foreground_popularity: 0.16667,"
+               + "             background_popularity: 0.5 },"
+               + "   } ] } } "
+               );
+    }
+    
+    // SKG used in multiple nested facets
+    //
+    // we'll re-use these params in 2 requests, one will simulate a shard request
+    final SolrParams nestedSKG = params
+      ("q", "cat_s:[* TO *]", "rows", "0", "fore", "num_i:[-1000 TO 0]", "back", "*:*", "json.facet"
+       , "{x: { type: terms, field: 'cat_s', sort: 'skg desc', "
+       + "      facet: { skg: 'relatedness($fore,$back)', "
+       + "               y:   { type: terms, field: 'where_s', sort: 'skg desc', "
+       + "                      facet: { skg: 'relatedness($fore,$back)' } } } } }");
+       
+    // plain old request
+    assertJQ(req(nestedSKG)
+             , "facets=={count:5, x:{ buckets:["
+             + "   { val:'B', count:3, "
+             + "     skg : { relatedness: 0.01539, "
+             //+ "             foreground_count: 2, "
+             //+ "             foreground_size: 2, "
+             //+ "             background_count: 3, "
+             //+ "             background_size: 6, "
+             + "             foreground_popularity: 0.33333,"
+             + "             background_popularity: 0.5 },"
+             + "     y : { buckets:["
+             + "            {  val:'NY', count: 1, "
+             + "               skg : { relatedness: 0.00554, " 
+             //+ "                       foreground_count: 1, "
+             //+ "                       foreground_size: 2, "
+             //+ "                       background_count: 2, "
+             //+ "                       background_size: 6, "
+             + "                       foreground_popularity: 0.16667, "
+             + "                       background_popularity: 0.33333, "
+             + "            } }, "
+             + "            {  val:'NJ', count: 2, "
+             + "               skg : { relatedness: 0.0, " // perfectly average and uncorrolated
+             //+ "                       foreground_count: 1, "
+             //+ "                       foreground_size: 2, "
+             //+ "                       background_count: 3, "
+             //+ "                       background_size: 6, "
+             + "                       foreground_popularity: 0.16667, "
+             + "                       background_popularity: 0.5, "
+             + "            } }, "
+             + "     ] } "
+             + "   }, "
+             + "   { val:'A', count:2, "
+             + "     skg : { relatedness:-0.01097, "
+             //+ "             foreground_count: 0, "
+             //+ "             foreground_size: 2, "
+             //+ "             background_count: 2, "
+             //+ "             background_size: 6,"
+             + "             foreground_popularity: 0.0,"
+             + "             background_popularity: 0.33333 },"
+             + "     y : { buckets:["
+             + "            {  val:'NJ', count: 1, "
+             + "               skg : { relatedness: 0.0, " // perfectly average and uncorrolated
+             //+ "                       foreground_count: 0, "
+             //+ "                       foreground_size: 0, "
+             //+ "                       background_count: 3, "
+             //+ "                       background_size: 6, "
+             + "                       foreground_popularity: 0.0, "
+             + "                       background_popularity: 0.5, "
+             + "            } }, "
+             + "            {  val:'NY', count: 1, "
+             + "               skg : { relatedness: 0.0, " // perfectly average and uncorrolated
+             //+ "                       foreground_count: 0, "
+             //+ "                       foreground_size: 0, "
+             //+ "                       background_count: 2, "
+             //+ "                       background_size: 6, "
+             + "                       foreground_popularity: 0.0, "
+             + "                       background_popularity: 0.33333, "
+             + "            } }, "
+             + "   ] } } ] } } ");
+
+    // same request, but with whitebox params testing isShard
+    // to verify the raw counts/sizes
+    assertJQ(req(nestedSKG,
+                 // fake an initial shard request
+                 "distrib", "false", "isShard", "true", "_facet_", "{}", "shards.purpose", "2097216")
+             , "facets=={count:5, x:{ buckets:["
+             + "   { val:'B', count:3, "
+             + "     skg : { "
+             + "             foreground_count: 2, "
+             + "             foreground_size: 2, "
+             + "             background_count: 3, "
+             + "             background_size: 6 }, "
+             + "     y : { buckets:["
+             + "            {  val:'NY', count: 1, "
+             + "               skg : { " 
+             + "                       foreground_count: 1, "
+             + "                       foreground_size: 2, "
+             + "                       background_count: 2, "
+             + "                       background_size: 6, "
+             + "            } }, "
+             + "            {  val:'NJ', count: 2, "
+             + "               skg : { " 
+             + "                       foreground_count: 1, "
+             + "                       foreground_size: 2, "
+             + "                       background_count: 3, "
+             + "                       background_size: 6, "
+             + "            } }, "
+             + "     ] } "
+             + "   }, "
+             + "   { val:'A', count:2, "
+             + "     skg : { " 
+             + "             foreground_count: 0, "
+             + "             foreground_size: 2, "
+             + "             background_count: 2, "
+             + "             background_size: 6 },"
+             + "     y : { buckets:["
+             + "            {  val:'NJ', count: 1, "
+             + "               skg : { " 
+             + "                       foreground_count: 0, "
+             + "                       foreground_size: 0, "
+             + "                       background_count: 3, "
+             + "                       background_size: 6, "
+             + "            } }, "
+             + "            {  val:'NY', count: 1, "
+             + "               skg : { " 
+             + "                       foreground_count: 0, "
+             + "                       foreground_size: 0, "
+             + "                       background_count: 2, "
+             + "                       background_size: 6, "
+             + "            } }, "
+             + "   ] } } ] } } ");
+    
+  }
+
+  @Test
   public void testRepeatedNumerics() throws Exception {
     Client client = Client.localClient();
     String field = "num_is"; // docValues of multi-valued points field can contain duplicate values... make sure they don't mess up our counts.

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/solr-ref-guide/src/json-facet-api.adoc
----------------------------------------------------------------------
diff --git a/solr/solr-ref-guide/src/json-facet-api.adoc b/solr/solr-ref-guide/src/json-facet-api.adoc
index 4f0ec7d..8250117 100644
--- a/solr/solr-ref-guide/src/json-facet-api.adoc
+++ b/solr/solr-ref-guide/src/json-facet-api.adoc
@@ -1,4 +1,5 @@
 = JSON Facet API
+:page-tocclass: right
 
 [[JSONFacetAPI]]
 == Facet & Analytics Module
@@ -338,17 +339,18 @@ Aggregation functions, also called *facet functions, analytic functions,* or **m
 [width="100%",cols="10%,30%,60%",options="header",]
 |===
 |Aggregation |Example |Description
-|sum |sum(sales) |summation of numeric values
-|avg |avg(popularity) |average of numeric values
-|min |min(salary) |minimum value
-|max |max(mul(price,popularity)) |maximum value
-|unique |unique(author) |number of unique values of the given field. Beyond 100 values it yields not exact estimate 
-|uniqueBlock |uniqueBlock(\_root_) |same as above with smaller footprint strictly requires <<uploading-data-with-index-handlers.adoc#nested-child-documents, block index>>. The given field is expected to be unique across blocks, now only singlevalued string fields are supported, docValues are recommended. 
-|hll |hll(author) |distributed cardinality estimate via hyper-log-log algorithm
-|percentile |percentile(salary,50,75,99,99.9) |Percentile estimates via t-digest algorithm. When sorting by this metric, the first percentile listed is used as the sort value.
-|sumsq |sumsq(rent) |sum of squares of field or function
-|variance |variance(rent) |variance of numeric field or function
-|stddev |stddev(rent) |standard deviation of field or function
+|sum |`sum(sales)` |summation of numeric values
+|avg |`avg(popularity)` |average of numeric values
+|min |`min(salary)` |minimum value
+|max |`max(mul(price,popularity))` |maximum value
+|unique |`unique(author)` |number of unique values of the given field. Beyond 100 values it yields not exact estimate 
+|uniqueBlock |`uniqueBlock(\_root_)` |same as above with smaller footprint strictly requires <<uploading-data-with-index-handlers.adoc#nested-child-documents, block index>>. The given field is expected to be unique across blocks, now only singlevalued string fields are supported, docValues are recommended. 
+|hll |`hll(author)` |distributed cardinality estimate via hyper-log-log algorithm
+|percentile |`percentile(salary,50,75,99,99.9)` |Percentile estimates via t-digest algorithm. When sorting by this metric, the first percentile listed is used as the sort value.
+|sumsq |`sumsq(rent)` |sum of squares of field or function
+|variance |`variance(rent)` |variance of numeric field or function
+|stddev |`stddev(rent)` |standard deviation of field or function
+|relatedness |`relatedness('popularity:[100 TO \*]','inStock:true')`|A function for computing a relatedness score of the documents in the domain to a Foreground set, relative to a Background set (both defined as queries).  This is primarily for use when building <<Semantic Knowledge Graphs>>.
 |===
 
 Numeric aggregation functions such as `avg` can be on any numeric field, or on another function of multiple numeric fields such as `avg(mul(price,popularity))`.
@@ -514,6 +516,126 @@ Aggregation `uniqueBlock(\_root_)` is functionally equivalent to `unique(\_root_
 It's recommended to define `limit: -1` for `uniqueBlock` calculation, like in above example,
 since default value of `limit` parameter is `10`, while `uniqueBlock` is supposed to be much faster with `-1`.
 
+== Semantic Knowledge Graphs
+
+The `relatedness(...)` aggregation functions allows for sets of documents to be scored relative to Foreground and Background sets of documents, for the purposes of finding ad-hoc relationships that make up a "Semantic Knowledge Graph":
+
+[quote, Grainger et al., 'https://arxiv.org/abs/1609.00464[The Semantic Knowledge Graph]']
+____
+At its heart, the Semantic Knowledge Graph leverages an inverted index, along with a complementary uninverted index, to represent nodes (terms) and edges (the documents within intersecting postings lists for multiple terms/nodes). This provides a layer of indirection between each pair of nodes and their corresponding edge, enabling edges to materialize dynamically from underlying corpus statistics. As a result, any combination of nodes can have edges to any other nodes materialize and be scored to reveal latent relationships between the nodes.
+____
+
+The `relatedness(...)` function is used to "score" these relationships, relative to "Foreground" and "Background" sets of documents, specified in the function params as queries.
+
+Unlike most aggregation functions, the `relatedness(...)` function is aware of if/how it's used in <<NestedFacets,Nested Facets>>.  It evaluates the query defining the current bucket _independently_ from it's parent/ancestor buckets, and intersects those documents with a "Foreground Set" defined by the foreground query _combined with the ancestor buckets_.  The result is then compared to a similar intersection done against the "Background Set" (defined exclusively by background query) to see if there is a positive, or negative, correlation between the current bucket and the Foreground Set, relative to the Background Set.
+
+=== Semantic Knowledge Graph Example
+
+
+.Sample Documents
+[source,bash,subs="verbatim,callouts"]
+----
+curl -sS -X POST 'http://localhost:8983/solr/gettingstarted/update?commit=true' -d '[
+{"id":"01",age:15,"state":"AZ","hobbies":["soccer","painting","cycling"]},
+{"id":"02",age:22,"state":"AZ","hobbies":["swimming","darts","cycling"]},
+{"id":"03",age:27,"state":"AZ","hobbies":["swimming","frisbee","painting"]},
+{"id":"04",age:33,"state":"AZ","hobbies":["darts"]},
+{"id":"05",age:42,"state":"AZ","hobbies":["swimming","golf","painting"]},
+{"id":"06",age:54,"state":"AZ","hobbies":["swimming","golf"]},
+{"id":"07",age:67,"state":"AZ","hobbies":["golf","painting"]},
+{"id":"08",age:71,"state":"AZ","hobbies":["painting"]},
+{"id":"09",age:14,"state":"CO","hobbies":["soccer","frisbee","skiing","swimming","skating"]},
+{"id":"10",age:23,"state":"CO","hobbies":["skiing","darts","cycling","swimming"]},
+{"id":"11",age:26,"state":"CO","hobbies":["skiing","golf"]},
+{"id":"12",age:35,"state":"CO","hobbies":["golf","frisbee","painting","skiing"]},
+{"id":"13",age:47,"state":"CO","hobbies":["skiing","darts","painting","skating"]},
+{"id":"14",age:51,"state":"CO","hobbies":["skiing","golf"]},
+{"id":"15",age:64,"state":"CO","hobbies":["skating","cycling"]},
+{"id":"16",age:73,"state":"CO","hobbies":["painting"]},
+]'
+----
+
+.Example Query
+[source,bash,subs="verbatim,callouts"]
+----
+curl -sS -X POST http://localhost:8983/solr/gettingstarted/query -d 'rows=0&q=*:*
+&back=*:*                                  # <1>
+&fore=age:[35 TO *]                        # <2>
+&json.facet={
+  hobby : {
+    type : terms,
+    field : hobbies,
+    limit : 5,
+    sort : { r1: desc },                   # <3>
+    facet : {
+      r1 : "relatedness($fore,$back)",     # <4>
+      location : {
+        type : terms,
+        field : state,
+        limit : 2,
+        sort : { r2: desc },               # <3>
+        facet : {
+          r2 : "relatedness($fore,$back)"  # <4>
+        }
+      }
+    }
+  }
+}'
+----
+<1> Use the entire collection as our "Background Set"
+<2> Use a query for "age >= 35" to define our (initial) "Foreground Set"
+<3> For both the top level `hobbies` facet & the sub-facet on `state` we will be sorting on the `relatedness(...)` values
+<4> In both calls to the `relatedness(...)` function, we use <<local-parameters-in-queries.adoc#parameter-dereferencing,Parameter Variables>> to refer to the previously defined `fore` and `back` queries. 
+
+.The Facet Response
+[source,javascript,subs="verbatim,callouts"]
+----
+"facets":{
+  "count":16,
+  "hobby":{
+    "buckets":[{
+        "val":"golf",
+        "count":6,                                // <1>
+        "r1":{
+          "relatedness":0.01225,
+          "foreground_popularity":0.3125,         // <2>
+          "background_popularity":0.375},         // <3>
+        "location":{
+          "buckets":[{
+              "val":"az",
+              "count":3,
+              "r2":{
+                "relatedness":0.00496,            // <4>
+                "foreground_popularity":0.1875,   // <6>
+                "background_popularity":0.5}},    // <7>
+            {
+              "val":"co",
+              "count":3,
+              "r2":{
+                "relatedness":-0.00496,           // <5>
+                "foreground_popularity":0.125,
+                "background_popularity":0.5}}]}},
+      {
+        "val":"painting",
+        "count":8,                                // <1>
+        "r1":{
+          "relatedness":0.01097,
+          "foreground_popularity":0.375,
+          "background_popularity":0.5},
+        "location":{
+          "buckets":[{
+            ...
+----
+<1> Even though `hobbies:golf` has a lower total facet `count` then `hobbies:painting`, it has a higher `relatedness` score, indicating that relative to the Background Set (the entire collection) Golf has a stronger correlation to our Foreground Set (people age 35+) then Painting. 
+<2> The number of documents matching `age:[35 TO *]` _and_ `hobbies:golf` is 31.25% of the total number of documents in the Background Set
+<3> 37.5% of the documents in the Background Set match `hobbies:golf`
+<4> The state of Arizona (AZ) has a _positive_ relatedness correlation with the _nested_ Foreground Set (people ages 35+ who play Golf) compared to the Background Set -- ie: "People in Arizona are statistically more likely to be '35+ year old Golfers' then the country as a whole."
+<5> The state of Colorado (CO) has a _negative_ correlation with the nested Foreground Set -- ie: "People in Colorado are statistically less likely to be '35+ year old Golfers' then the country as a whole."
+<6> The number documents matching `age:[35 TO *]` _and_ `hobbies:golf` _and_ `state:AZ` is 18.75% of the total number of documents in the Background Set
+<7> 50% of the documents in the Background Set match `state:AZ`
+
+NOTE: While it's very common to define the Background Set as `\*:*`, or some other super-set of the Foreground Query, it is not strictly required.  The `relatedness(...)` function can be used to compare the statistical relatedness of sets of documents to orthogonal foreground/background queries.
+
 [[References]]
 == References
 


[2/2] lucene-solr:master: SOLR-9480: A new 'relatedness()' aggregate function for JSON Faceting to enable building Semantic Knowledge Graphs

Posted by ho...@apache.org.
SOLR-9480: A new 'relatedness()' aggregate function for JSON Faceting to enable building Semantic Knowledge Graphs


Project: http://git-wip-us.apache.org/repos/asf/lucene-solr/repo
Commit: http://git-wip-us.apache.org/repos/asf/lucene-solr/commit/669b9e7a
Tree: http://git-wip-us.apache.org/repos/asf/lucene-solr/tree/669b9e7a
Diff: http://git-wip-us.apache.org/repos/asf/lucene-solr/diff/669b9e7a

Branch: refs/heads/master
Commit: 669b9e7a5343c625e265a075c9dbf24fcbff7363
Parents: 0c0fce3
Author: Chris Hostetter <ho...@apache.org>
Authored: Mon May 21 08:22:54 2018 -0700
Committer: Chris Hostetter <ho...@apache.org>
Committed: Mon May 21 08:22:54 2018 -0700

----------------------------------------------------------------------
 solr/CHANGES.txt                                |   3 +
 .../apache/solr/search/ValueSourceParser.java   |  12 +
 .../apache/solr/search/facet/FacetField.java    |   2 +-
 .../solr/search/facet/FacetFieldProcessor.java  |  43 +-
 .../facet/FacetFieldProcessorByArray.java       |  25 +-
 .../facet/FacetFieldProcessorByArrayDV.java     |   4 +-
 .../FacetFieldProcessorByEnumTermsStream.java   |  17 +-
 .../facet/FacetFieldProcessorByHashDV.java      |  10 +-
 .../apache/solr/search/facet/FacetMerger.java   |   6 +-
 .../solr/search/facet/FacetProcessor.java       |  61 +-
 .../apache/solr/search/facet/FacetRange.java    |   3 +-
 .../apache/solr/search/facet/FacetRequest.java  |  53 +-
 .../search/facet/FacetRequestSortedMerger.java  |   2 +-
 .../org/apache/solr/search/facet/HLLAgg.java    |   3 +-
 .../org/apache/solr/search/facet/MinMaxAgg.java |   9 +-
 .../apache/solr/search/facet/PercentileAgg.java |   3 +-
 .../solr/search/facet/RelatednessAgg.java       | 449 +++++++++++++
 .../org/apache/solr/search/facet/SlotAcc.java   |  74 ++-
 .../solr/search/facet/UnInvertedField.java      |   8 +-
 .../org/apache/solr/search/facet/UniqueAgg.java |   3 +-
 .../solr/search/facet/UniqueMultiDvSlotAcc.java |   3 +-
 .../search/facet/UniqueMultivaluedSlotAcc.java  |   5 +-
 .../search/facet/UniqueSinglevaluedSlotAcc.java |   3 +-
 .../solr/cloud/TestCloudJSONFacetSKG.java       | 654 +++++++++++++++++++
 .../apache/solr/search/QueryEqualityTest.java   |  10 +
 .../org/apache/solr/search/facet/DebugAgg.java  |   9 +-
 ...ibutedFacetSimpleRefinementLongTailTest.java |  19 +-
 .../search/facet/TestJsonFacetRefinement.java   |  69 ++
 .../solr/search/facet/TestJsonFacets.java       | 239 +++++++
 solr/solr-ref-guide/src/json-facet-api.adoc     | 144 +++-
 30 files changed, 1848 insertions(+), 97 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/CHANGES.txt
----------------------------------------------------------------------
diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 1a43328..38cd545 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -116,6 +116,9 @@ New Features
 
 * SOLR-11277: Add auto hard-commit settings based on tlog size (Rupa Shankar, Anshum Gupta)
 
+* SOLR-9480: A new 'relatedness()' aggregate function for JSON Faceting to enable building Semantic
+  Knowledge Graphs. (Trey Grainger, hossman)
+
 Bug Fixes
 ----------------------
 

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/ValueSourceParser.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/ValueSourceParser.java b/solr/core/src/java/org/apache/solr/search/ValueSourceParser.java
index 683cf4a..b7c6815 100644
--- a/solr/core/src/java/org/apache/solr/search/ValueSourceParser.java
+++ b/solr/core/src/java/org/apache/solr/search/ValueSourceParser.java
@@ -63,6 +63,7 @@ import org.apache.solr.search.facet.PercentileAgg;
 import org.apache.solr.search.facet.StddevAgg;
 import org.apache.solr.search.facet.SumAgg;
 import org.apache.solr.search.facet.SumsqAgg;
+import org.apache.solr.search.facet.RelatednessAgg;
 import org.apache.solr.search.facet.UniqueAgg;
 import org.apache.solr.search.facet.UniqueBlockAgg;
 import org.apache.solr.search.facet.VarianceAgg;
@@ -1039,6 +1040,17 @@ public abstract class ValueSourceParser implements NamedListInitializedPlugin {
 
     addParser("agg_percentile", new PercentileAgg.Parser());
     
+    addParser("agg_" + RelatednessAgg.NAME, new ValueSourceParser() {
+      @Override
+      public ValueSource parse(FunctionQParser fp) throws SyntaxError {
+        // TODO: (fore & back)-ground should be optional -- use hasMoreArguments
+        // if only one arg, assume it's the foreground
+        // (background is the one that will most commonly just be "*:*")
+        // see notes in RelatednessAgg constructor about why we don't do this yet
+        return new RelatednessAgg(fp.parseNestedQuery(), fp.parseNestedQuery());
+      }
+    });
+    
     addParser("childfield", new ChildFieldValueSourceParser());
   }
 

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetField.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetField.java b/solr/core/src/java/org/apache/solr/search/facet/FacetField.java
index 1a59549..4de0411 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetField.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetField.java
@@ -42,7 +42,7 @@ abstract class FacetRequestSorted extends FacetRequest {
 
   @Override
   public boolean returnsPartial() {
-    return limit > 0;
+    return super.returnsPartial() || (limit > 0);
   }
 
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessor.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessor.java b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessor.java
index f872db3..7276593 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessor.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessor.java
@@ -36,6 +36,7 @@ import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.schema.FieldType;
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.DocSet;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 
 import static org.apache.solr.search.facet.FacetContext.SKIP_FACET;
 
@@ -226,23 +227,23 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
     }
   }
 
-  int collectFirstPhase(DocSet docs, int slot) throws IOException {
+  int collectFirstPhase(DocSet docs, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     int num = -1;
     if (collectAcc != null) {
-      num = collectAcc.collect(docs, slot);
+      num = collectAcc.collect(docs, slot, slotContext);
     }
     if (allBucketsAcc != null) {
-      num = allBucketsAcc.collect(docs, slot);
+      num = allBucketsAcc.collect(docs, slot, slotContext);
     }
     return num >= 0 ? num : docs.size();
   }
 
-  void collectFirstPhase(int segDoc, int slot) throws IOException {
+  void collectFirstPhase(int segDoc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     if (collectAcc != null) {
-      collectAcc.collect(segDoc, slot);
+      collectAcc.collect(segDoc, slot, slotContext);
     }
     if (allBucketsAcc != null) {
-      allBucketsAcc.collect(segDoc, slot);
+      allBucketsAcc.collect(segDoc, slot, slotContext);
     }
   }
 
@@ -373,7 +374,7 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
       Comparable val = bucketValFromSlotNumFunc.apply(slotNum);
       bucket.add("val", val);
 
-      Query filter = needFilter ? sf.getType().getFieldQuery(null, sf, fieldQueryValFunc.apply(val)) : null;
+      Query filter = needFilter ? makeBucketQuery(fieldQueryValFunc.apply(val)) : null;
 
       fillBucket(bucket, countAcc.getCount(slotNum), slotNum, null, filter);
 
@@ -388,6 +389,15 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
     return res;
   }
 
+  /**
+   * Trivial helper method for building up a bucket query given the (Stringified) bucket value
+   */
+  protected Query makeBucketQuery(final String bucketValue) {
+    // TODO: this isn't viable for things like text fields w/ analyzers that are non-idempotent (ie: stemmers)
+    // TODO: but changing it to just use TermQuery isn't safe for things like numerics, dates, etc...
+    return sf.getType().getFieldQuery(null, sf, bucketValue);
+  }
+
   private void calculateNumBuckets(SimpleOrderedMap<Object> target) throws IOException {
     DocSet domain = fcontext.base;
     if (freq.prefix != null) {
@@ -397,7 +407,7 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
 
     HLLAgg agg = new HLLAgg(freq.field);
     SlotAcc acc = agg.createSlotAcc(fcontext, domain.size(), 1);
-    acc.collect(domain, 0);
+    acc.collect(domain, 0, null); // we know HLL doesn't care about the bucket query
     acc.key = "numBuckets";
     acc.setValues(target, 0);
   }
@@ -433,7 +443,7 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
       // do acc at a time (traversing domain each time) or do all accs for each doc?
       for (SlotAcc acc : otherAccs) {
         acc.reset(); // TODO: only needed if we previously used for allBuckets or missing
-        acc.collect(subDomain, 0);
+        acc.collect(subDomain, 0, slot -> { return new SlotContext(filter); });
         acc.setValues(target, 0);
       }
     }
@@ -442,13 +452,14 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
   }
 
   @Override
-  protected void processStats(SimpleOrderedMap<Object> bucket, DocSet docs, int docCount) throws IOException {
+  protected void processStats(SimpleOrderedMap<Object> bucket, Query bucketQ, DocSet docs, int docCount) throws IOException {
     if (docCount == 0 && !freq.processEmpty || freq.getFacetStats().size() == 0) {
       bucket.add("count", docCount);
       return;
     }
     createAccs(docCount, 1);
-    int collected = collect(docs, 0);
+    assert null != bucketQ;
+    int collected = collect(docs, 0, slotNum -> { return new SlotContext(bucketQ); });
 
     // countAcc.incrementCount(0, collected);  // should we set the counton the acc instead of just passing it?
 
@@ -499,9 +510,9 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
     }
 
     @Override
-    public void collect(int doc, int slot) throws IOException {
+    public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
       for (SlotAcc acc : subAccs) {
-        acc.collect(doc, slot);
+        acc.collect(doc, slot, slotContext);
       }
     }
 
@@ -561,15 +572,15 @@ abstract class FacetFieldProcessor extends FacetProcessor<FacetField> {
     }
 
     @Override
-    public void collect(int doc, int slot) throws IOException {
+    public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
       assert slot != collectAccSlot || slot < 0;
       count++;
       if (collectAcc != null) {
-        collectAcc.collect(doc, collectAccSlot);
+        collectAcc.collect(doc, collectAccSlot, slotContext);
       }
       if (otherAccs != null) {
         for (SlotAcc otherAcc : otherAccs) {
-          otherAcc.collect(doc, otherAccsSlot);
+          otherAcc.collect(doc, otherAccsSlot, slotContext);
         }
       }
     }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArray.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArray.java b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArray.java
index 43bafd4..e5ee181 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArray.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArray.java
@@ -19,11 +19,14 @@ package org.apache.solr.search.facet;
 
 import java.io.IOException;
 import java.util.Date;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.BytesRefBuilder;
+import org.apache.lucene.search.Query;
 import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.schema.SchemaField;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 
 import static org.apache.solr.search.facet.FacetContext.SKIP_FACET;
 
@@ -116,8 +119,28 @@ abstract class FacetFieldProcessorByArray extends FacetFieldProcessor {
             throw new RuntimeException(e);
           }
         },
-        obj -> obj instanceof Date ? ((Date)obj).toInstant().toString() : obj.toString()
+        obj -> valueObjToString(obj)
     );
   }
 
+  private static String valueObjToString(Object obj) {
+    return (obj instanceof Date) ? ((Date)obj).toInstant().toString() : obj.toString();
+  }
+
+                                                           
+  /**
+   * SlotContext to use during all {@link SlotAcc} collection.
+   *
+   * @see #lookupOrd
+   */
+  public IntFunction<SlotContext> slotContext = (slotNum) -> {
+    try {
+      Object value = sf.getType().toObject(sf, lookupOrd(slotNum));
+      Query q = makeBucketQuery(valueObjToString(value));
+      assert null != q : "null query for: '" + value + "'";
+      return new SlotContext(q);
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  };
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArrayDV.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArrayDV.java b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArrayDV.java
index fe7a3f2..4a0d13e 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArrayDV.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByArrayDV.java
@@ -327,10 +327,10 @@ class FacetFieldProcessorByArrayDV extends FacetFieldProcessorByArray {
     if (arrIdx >= 0 && arrIdx < nTerms) {
       countAcc.incrementCount(arrIdx, 1);
       if (collectAcc != null) {
-        collectAcc.collect(doc, arrIdx);
+        collectAcc.collect(doc, arrIdx, slotContext);
       }
       if (allBucketsAcc != null) {
-        allBucketsAcc.collect(doc, arrIdx);
+        allBucketsAcc.collect(doc, arrIdx, slotContext);
       }
     }
   }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByEnumTermsStream.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByEnumTermsStream.java b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByEnumTermsStream.java
index bbc2973..f939bba 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByEnumTermsStream.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByEnumTermsStream.java
@@ -21,6 +21,7 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.util.Iterator;
 import java.util.List;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiPostingsEnum;
@@ -40,6 +41,7 @@ import org.apache.solr.search.DocSet;
 import org.apache.solr.search.HashDocSet;
 import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.search.SortedIntDocSet;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 
 /**
  * Enumerates indexed terms in order in a streaming fashion.
@@ -60,6 +62,13 @@ class FacetFieldProcessorByEnumTermsStream extends FacetFieldProcessor implement
   PostingsEnum postingsEnum;
   BytesRef startTermBytes;
   BytesRef term;
+
+  // at any point in processing where we need a SlotContext, all we care about is the current 'term'
+  private IntFunction<SlotContext> slotContext = (slotNum) -> {
+    assert null != term;
+    return new SlotAcc.SlotContext(new TermQuery(new Term(sf.getName(), term)));
+  };
+  
   LeafReaderContext[] leaves;
 
   FacetFieldProcessorByEnumTermsStream(FacetContext fcontext, FacetField freq, SchemaField sf) {
@@ -195,7 +204,7 @@ class FacetFieldProcessorByEnumTermsStream extends FacetFieldProcessor implement
 
   private SimpleOrderedMap<Object> _nextBucket() throws IOException {
     DocSet termSet = null;
-
+    
     try {
       while (term != null) {
 
@@ -241,7 +250,7 @@ class FacetFieldProcessorByEnumTermsStream extends FacetFieldProcessor implement
             resetStats();
 
             if (!countOnly) {
-              collect(termSet, 0);
+              collect(termSet, 0, slotContext);
             }
 
         } else {
@@ -278,7 +287,7 @@ class FacetFieldProcessorByEnumTermsStream extends FacetFieldProcessor implement
                 while ((docid = sub.postingsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
                   if (fastForRandomSet.exists(docid + base)) {
                     c++;
-                    collect(docid, 0);
+                    collect(docid, 0, slotContext);
                   }
                 }
               }
@@ -295,7 +304,7 @@ class FacetFieldProcessorByEnumTermsStream extends FacetFieldProcessor implement
               while ((docid = postingsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
                 if (fastForRandomSet.exists(docid)) {
                   c++;
-                  collect(docid, 0);
+                  collect(docid, 0, slotContext);
                 }
               }
             }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByHashDV.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByHashDV.java b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByHashDV.java
index 0cafd3a..4c0b244 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByHashDV.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetFieldProcessorByHashDV.java
@@ -37,6 +37,7 @@ import org.apache.solr.common.SolrException;
 import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.DocSetUtil;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 
 /**
  * Facets numbers into a hash table.  The number is either a raw numeric DocValues value, or
@@ -260,7 +261,7 @@ class FacetFieldProcessorByHashDV extends FacetFieldProcessor {
 
     indexOrderAcc = new SlotAcc(fcontext) {
       @Override
-      public void collect(int doc, int slot) throws IOException {
+      public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
       }
 
       @Override
@@ -306,7 +307,7 @@ class FacetFieldProcessorByHashDV extends FacetFieldProcessor {
       }
 
       @Override
-      public void collect(int doc, int slot) throws IOException {
+      public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
         throw new UnsupportedOperationException();
       }
 
@@ -429,7 +430,10 @@ class FacetFieldProcessorByHashDV extends FacetFieldProcessor {
     // Our countAcc is virtual, so this is not needed:
     // countAcc.incrementCount(slot, 1);
 
-    super.collectFirstPhase(segDoc, slot);
+    super.collectFirstPhase(segDoc, slot, slotNum -> {
+        Comparable value = calc.bitsToValue(val);
+        return new SlotContext(sf.getType().getFieldQuery(null, sf, calc.formatValue(value)));
+      });
   }
 
   private void doRehash(LongCounts table) {

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetMerger.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetMerger.java b/solr/core/src/java/org/apache/solr/search/facet/FacetMerger.java
index 9499d2c..84ffbf0 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetMerger.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetMerger.java
@@ -120,8 +120,10 @@ public abstract class FacetMerger {
 
       subs = null;
       for (Map.Entry<String,FacetRequest> entry : freq.subFacets.entrySet()) {
-        Collection<String> childSubs = getSubsWithPartial(entry.getValue());
-        if (childSubs.size() > 0 || entry.getValue().returnsPartial()) {
+        final FacetRequest entryVal = entry.getValue();
+        Collection<String> childSubs = getSubsWithPartial(entryVal);
+        // TODO: should returnsPartial() check processEmpty internally?
+        if (childSubs.size() > 0 || entryVal.returnsPartial() || entryVal.processEmpty) {
           if (subs == null) {
             subs = new ArrayList<>(freq.getSubFacets().size());
           }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetProcessor.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetProcessor.java b/solr/core/src/java/org/apache/solr/search/facet/FacetProcessor.java
index 27cdaec..c0625df 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetProcessor.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetProcessor.java
@@ -24,6 +24,7 @@ import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.BooleanClause;
@@ -42,6 +43,7 @@ import org.apache.solr.search.QParser;
 import org.apache.solr.search.QueryContext;
 import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.search.SyntaxError;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 import org.apache.solr.util.RTimer;
 
 public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
@@ -78,6 +80,7 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
   FacetProcessor(FacetContext fcontext, FacetRequestT freq) {
     this.fcontext = fcontext;
     this.freq = freq;
+    fcontext.processor = this;
   }
 
   public Object getResponse() {
@@ -90,10 +93,13 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
 
   private void evalFilters() throws IOException {
     if (freq.domain.filters == null || freq.domain.filters.isEmpty()) return;
-
-    List<Query> qlist = new ArrayList<>(freq.domain.filters.size());
+    this.filter = fcontext.searcher.getDocSet(evalJSONFilterQueryStruct(fcontext, freq.domain.filters));
+  }
+  
+  private static List<Query> evalJSONFilterQueryStruct(FacetContext fcontext, List<Object> filters) throws IOException {
+    List<Query> qlist = new ArrayList<>(filters.size());
     // TODO: prevent parsing filters each time!
-    for (Object rawFilter : freq.domain.filters) {
+    for (Object rawFilter : filters) {
       if (rawFilter instanceof String) {
         QParser parser = null;
         try {
@@ -149,13 +155,30 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
       }
 
     }
-
-    this.filter = fcontext.searcher.getDocSet(qlist);
+    return qlist;
   }
 
   private void handleDomainChanges() throws IOException {
     if (freq.domain == null) return;
-    handleFilterExclusions();
+
+    if (null != freq.domain.explicitQueries) {
+      try {
+        final List<Query> domainQs = evalJSONFilterQueryStruct(fcontext, freq.domain.explicitQueries);
+        if (domainQs.isEmpty()) {
+          throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+                                  "'query' domain must not evaluate to an empty list of queries");
+        }
+        fcontext.base = fcontext.searcher.getDocSet(domainQs);
+      } catch (SolrException e) {
+        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+                                "Unable to parse domain 'query': " + freq.domain.explicitQueries +
+                                " -- reason: " + e.getMessage(),
+                                e);
+      }
+    } else {
+      // mutualy exclusive to freq.domain.explicitQueries
+      handleFilterExclusions();
+    }
 
     // Check filters... if we do have filters they apply after domain changes.
     // We still calculate them first because we can use it in a parent->child domain change.
@@ -277,13 +300,13 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
     return appliedFilters;
   }
 
-  protected void processStats(SimpleOrderedMap<Object> bucket, DocSet docs, int docCount) throws IOException {
+  protected void processStats(SimpleOrderedMap<Object> bucket, Query bucketQ, DocSet docs, int docCount) throws IOException {
     if (docCount == 0 && !freq.processEmpty || freq.getFacetStats().size() == 0) {
       bucket.add("count", docCount);
       return;
     }
     createAccs(docCount, 1);
-    int collected = collect(docs, 0);
+    int collected = collect(docs, 0, slotNum -> { return new SlotContext(bucketQ); });
     countAcc.incrementCount(0, collected);
     assert collected == docCount;
     addStats(bucket, 0);
@@ -319,10 +342,22 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
     }
   }
 
-  int collect(DocSet docs, int slot) throws IOException {
+  int collect(DocSet docs, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     int count = 0;
     SolrIndexSearcher searcher = fcontext.searcher;
 
+    if (0 == docs.size()) {
+      // we may be in a "processEmpty" type situation where the client still cares about this bucket
+      // either way, we should let our accumulators know about the empty set, so they can collect &
+      // compute the slot (ie: let them decide if they care even when it's size==0)
+      if (accs != null) {
+        for (SlotAcc acc : accs) {
+          acc.collect(docs, slot, slotContext); // NOT per-seg collectors
+        }
+      }
+      return count;
+    }
+    
     final List<LeafReaderContext> leaves = searcher.getIndexReader().leaves();
     final Iterator<LeafReaderContext> ctxIt = leaves.iterator();
     LeafReaderContext ctx = null;
@@ -346,15 +381,15 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
         setNextReader(ctx);
       }
       count++;
-      collect(doc - segBase, slot);  // per-seg collectors
+      collect(doc - segBase, slot, slotContext);  // per-seg collectors
     }
     return count;
   }
 
-  void collect(int segDoc, int slot) throws IOException {
+  void collect(int segDoc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     if (accs != null) {
       for (SlotAcc acc : accs) {
-        acc.collect(segDoc, slot);
+        acc.collect(segDoc, slot, slotContext);
       }
     }
   }
@@ -402,7 +437,7 @@ public abstract class FacetProcessor<FacetRequestT extends FacetRequest>  {
 
     try {
       if (!skip) {
-        processStats(bucket, result, count);
+        processStats(bucket, q, result, count);
       }
       processSubs(bucket, q, result, skip, facetInfo);
     } finally {

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetRange.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetRange.java b/solr/core/src/java/org/apache/solr/search/facet/FacetRange.java
index 09b8ec0..817ada6 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetRange.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetRange.java
@@ -38,6 +38,7 @@ import org.apache.solr.schema.SchemaField;
 import org.apache.solr.schema.TrieDateField;
 import org.apache.solr.schema.TrieField;
 import org.apache.solr.search.DocSet;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 import org.apache.solr.util.DateMathParser;
 
 import static org.apache.solr.search.facet.FacetContext.SKIP_FACET;
@@ -364,7 +365,7 @@ class FacetRangeProcessor extends FacetProcessor<FacetRange> {
     DocSet intersection = fcontext.searcher.getDocSet(rangeQ, fcontext.base);
     filters[slot] = rangeQ;
     intersections[slot] = intersection;  // save for later  // TODO: only save if number of slots is small enough?
-    int num = collect(intersection, slot);
+    int num = collect(intersection, slot, slotNum -> { return new SlotContext(rangeQ); });
     countAcc.incrementCount(slot, num); // TODO: roll this into collect()
   }
 

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetRequest.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetRequest.java b/solr/core/src/java/org/apache/solr/search/facet/FacetRequest.java
index 4cf8a68..6337bcb 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetRequest.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetRequest.java
@@ -87,6 +87,15 @@ public abstract class FacetRequest {
 
   // domain changes
   public static class Domain {
+    /** 
+     * An explicit query domain, <em>ignoring all parent context</em>, expressed in JSON query format.
+     * Mutually exclusive to {@link #excludeTags}
+     */
+    public List<Object> explicitQueries; // list of symbolic filters (JSON query format)
+    /**
+     * Specifies query/filter tags that should be excluded to re-compute the domain from the parent context.
+     * Mutually exclusive to {@link #explicitQueries}
+     */
     public List<String> excludeTags;
     public JoinField joinField;
     public boolean toParent;
@@ -96,12 +105,13 @@ public abstract class FacetRequest {
 
     // True if a starting set of documents can be mapped onto a different set of documents not originally in the starting set.
     public boolean canTransformDomain() {
-      return toParent || toChildren || (excludeTags != null) || (joinField != null);
+      return toParent || toChildren
+        || (explicitQueries != null) || (excludeTags != null) || (joinField != null);
     }
 
     // Can this domain become non-empty if the input domain is empty?  This does not check any sub-facets (see canProduceFromEmpty for that)
     public boolean canBecomeNonEmpty() {
-      return excludeTags != null;
+      return (explicitQueries != null) || (excludeTags != null);
     }
 
     /** Are we doing a query time join across other documents */
@@ -197,6 +207,7 @@ public abstract class FacetRequest {
    * This is normally true only for facets with a limit.
    */
   public boolean returnsPartial() {
+    // TODO: should the default impl check processEmpty ?
     return false;
   }
 
@@ -242,6 +253,7 @@ class FacetContext {
   public static final int IS_REFINEMENT=0x02;
   public static final int SKIP_FACET=0x04;  // refinement: skip calculating this immediate facet, but proceed to specific sub-facets based on facetInfo
 
+  FacetProcessor processor;
   Map<String,Object> facetInfo; // refinement info for this node
   QueryContext qcontext;
   SolrQueryRequest req;  // TODO: replace with params?
@@ -459,6 +471,17 @@ abstract class FacetParser<FacetRequestT extends FacetRequest> {
           domain.excludeTags = excludeTags;
         }
 
+        if (domainMap.containsKey("query")) {
+          domain.explicitQueries = parseJSONQueryStruct(domainMap.get("query"));
+          if (null == domain.explicitQueries) {
+            throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+                                    "'query' domain can not be null or empty");
+          } else if (null != domain.excludeTags) {
+            throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+                                    "'query' domain can not be combined with 'excludeTags'");
+          }
+        }
+        
         String blockParent = (String)domainMap.get("blockParent");
         String blockChildren = (String)domainMap.get("blockChildren");
 
@@ -475,21 +498,29 @@ abstract class FacetParser<FacetRequestT extends FacetRequest> {
         Object filterOrList = domainMap.get("filter");
         if (filterOrList != null) {
           assert domain.filters == null;
-          if (filterOrList instanceof List) {
-            domain.filters = (List<Object>)filterOrList;
-          } else {
-            domain.filters = new ArrayList<>(1);
-            domain.filters.add(filterOrList);
-          }
+          domain.filters = parseJSONQueryStruct(filterOrList);
         }
 
-
       } // end "domain"
-
-
     }
   }
 
+  /** returns null on null input, otherwise returns a list of the JSON query structures -- either
+   * directly from the raw (list) input, or if raw input is a not a list then it encapsulates 
+   * it in a new list.
+   */
+  private List<Object> parseJSONQueryStruct(Object raw) {
+    List<Object> result = null;
+    if (null == raw) {
+      return result;
+    } else if (raw instanceof List) {
+      result = (List<Object>) raw;
+    } else {
+      result = new ArrayList<>(1);
+      result.add(raw);
+    }
+    return result;
+  }
 
   public String getField(Map<String,Object> args) {
     Object fieldName = args.get("field"); // TODO: pull out into defined constant

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/FacetRequestSortedMerger.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/FacetRequestSortedMerger.java b/solr/core/src/java/org/apache/solr/search/facet/FacetRequestSortedMerger.java
index 9ffdea7..d737885 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/FacetRequestSortedMerger.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/FacetRequestSortedMerger.java
@@ -162,7 +162,7 @@ abstract class FacetRequestSortedMerger<FacetRequestT extends FacetRequestSorted
 
     // TODO: add information in sub-shard response about dropped buckets (i.e. not all returned due to limit)
     // If we know we've seen all the buckets from a shard, then we don't have to add to leafBuckets or partialBuckets, only skipBuckets
-    boolean isCommandPartial = freq.returnsPartial();
+    boolean isCommandPartial = freq.returnsPartial() || freq.processEmpty; // TODO: should returnsPartial() check processEmpty internally?
     boolean returnedAllBuckets = !isCommandPartial && !thisMissing;  // did the shard return all of the possible buckets?
 
     if (returnedAllBuckets && tags.isEmpty() && tagsWithPartial.isEmpty()) {

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/HLLAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/HLLAgg.java b/solr/core/src/java/org/apache/solr/search/facet/HLLAgg.java
index 897dceb..4634bc2 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/HLLAgg.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/HLLAgg.java
@@ -17,6 +17,7 @@
 package org.apache.solr.search.facet;
 
 import java.io.IOException;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.SortedNumericDocValues;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -140,7 +141,7 @@ public class HLLAgg extends StrAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slot) throws IOException {
+    public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
       int valuesDocID = docIdSetIterator().docID();
       if (valuesDocID < doc) {
         valuesDocID = docIdSetIterator().advance(doc);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/MinMaxAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/MinMaxAgg.java b/solr/core/src/java/org/apache/solr/search/facet/MinMaxAgg.java
index 8d4dc4d..1c961e0 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/MinMaxAgg.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/MinMaxAgg.java
@@ -19,6 +19,7 @@ package org.apache.solr.search.facet;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Date;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiDocValues;
@@ -142,7 +143,7 @@ public class MinMaxAgg extends SimpleAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slotNum) throws IOException {
+    public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
       double val = values.doubleVal(doc);
       if (val == 0 && !values.exists(doc)) return; // depend on fact that non existing values return 0 for func query
 
@@ -171,7 +172,7 @@ public class MinMaxAgg extends SimpleAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slotNum) throws IOException {
+    public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
       long val = values.longVal(doc);
       if (val == 0 && !values.exists(doc)) return; // depend on fact that non existing values return 0 for func query
 
@@ -230,7 +231,7 @@ public class MinMaxAgg extends SimpleAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slotNum) throws IOException {
+    public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
       long val = values.longVal(doc);
       if (val == 0 && !values.exists(doc)) return; // depend on fact that non existing values return 0 for func query
 
@@ -334,7 +335,7 @@ public class MinMaxAgg extends SimpleAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slotNum) throws IOException {
+    public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
       if (subDv.advanceExact(doc)) {
         int segOrd = subDv.ordValue();
         int ord = toGlobal==null ? segOrd : (int)toGlobal.get(segOrd);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/PercentileAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/PercentileAgg.java b/solr/core/src/java/org/apache/solr/search/facet/PercentileAgg.java
index ea46a91..efdef55 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/PercentileAgg.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/PercentileAgg.java
@@ -21,6 +21,7 @@ import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.function.IntFunction;
 
 import com.tdunning.math.stats.AVLTreeDigest;
 import org.apache.lucene.queries.function.ValueSource;
@@ -109,7 +110,7 @@ public class PercentileAgg extends SimpleAggValueSource {
       digests = new AVLTreeDigest[numSlots];
     }
 
-    public void collect(int doc, int slotNum) throws IOException {
+    public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
       if (!values.exists(doc)) return;
       double val = values.doubleVal(doc);
 

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/RelatednessAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/RelatednessAgg.java b/solr/core/src/java/org/apache/solr/search/facet/RelatednessAgg.java
new file mode 100644
index 0000000..5bc1108
--- /dev/null
+++ b/solr/core/src/java/org/apache/solr/search/facet/RelatednessAgg.java
@@ -0,0 +1,449 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.search.facet;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.Map;
+import java.util.function.IntFunction;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.queries.function.FunctionValues;
+import org.apache.lucene.search.Query;
+
+import org.apache.solr.common.SolrException;
+import org.apache.solr.common.util.NamedList;
+import org.apache.solr.common.util.SimpleOrderedMap;
+import org.apache.solr.search.DocSet;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * An aggregation function designed to be nested under other (possibly deeply nested) facets for 
+ * the purposes of computing the "relatedness" of facet buckets relative to 
+ * "foreground" and "background" sets -- primarily for the purpose of building "Semantic Knowledge Graphs"
+ *
+ * @see <a href="https://arxiv.org/pdf/1609.00464.pdf">The Semantic Knowledge Graph: 
+ *     A compact, auto-generated model for real-time traversal and ranking of any relationship 
+ *     within a domain</a>
+ */
+public class RelatednessAgg extends AggValueSource {
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+  // end user values
+  private static final String RELATEDNESS = "relatedness";
+  private static final String FG_POP = "foreground_popularity";
+  private static final String BG_POP = "background_popularity";
+
+  // needed for distrib calculation
+  private static final String FG_SIZE = "foreground_size";
+  private static final String FG_COUNT = "foreground_count";
+  private static final String BG_SIZE = "background_size";
+  private static final String BG_COUNT = "background_count";
+  
+  final protected Query fgQ;
+  final protected Query bgQ;
+  
+  public static final String NAME = RELATEDNESS;
+  public RelatednessAgg(Query fgQ, Query bgQ) {
+    super(NAME); 
+    // NOTE: ideally we don't want to assume any defaults *yet* if fgQ/bgQ are null
+    // keep them null until it's time to created a SlotAcc, at which point we might inherit values
+    // from an ancestor facet context w/same key -- see comments in createSlotAcc
+    this.fgQ = fgQ;
+    this.bgQ = bgQ;
+
+    // TODO: defaults not supported yet -- see comments in createSlotAcc
+    if (null == fgQ || null == bgQ) {
+      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+                              NAME + " aggregate function requires both foreground & background " +
+                              "to be real (non-null) queries");
+    }
+  }
+
+  @Override
+  public String description() {
+    // TODO: need better output processing when we start supporting null fgQ/bgQ in constructor
+    return name +"(" + fgQ + "," + bgQ + ")";
+  }
+  
+  @Override
+  public boolean equals(Object o) {
+    if (! Objects.equals(this.getClass(), o.getClass())) {
+      return false;
+    }
+    RelatednessAgg that = (RelatednessAgg) o;
+    return Objects.equals(fgQ, that.fgQ) && Objects.equals(bgQ, that.bgQ);
+  }
+  
+  @Override
+  public int hashCode() {
+    return Objects.hash(getClass(), fgQ, bgQ);
+  }
+
+  @Override
+  public FunctionValues getValues(Map context, LeafReaderContext readerContext) throws IOException {
+    throw new UnsupportedOperationException("NOT IMPLEMENTED " + name + " " + this);
+  }
+
+
+  public SlotAcc createSlotAcc(FacetContext fcontext, int numDocs, int numSlots) throws IOException {
+    // TODO: Ideally this is where we should check fgQ/bgQ for 'null' and apply defaults...
+    //
+    // we want to walk up the fcontext and inherit the queries from any ancestor SKGAgg
+    // with the same "key" that we have in our own context -- and as a last resort use
+    // "$q" for the foreground and "*:*" for the bgQ (if no ancestors)
+    // (Hmmm... or maybe we should use the "Domain" of our FacetRequest as the default bg?)
+    //
+    // How do we find our what key we have in the current context?
+    // loop over all the stats in the current context until we find one that's '==' to this???
+    
+    List<Query> fgFilters = new ArrayList<Query>(3);
+    fgFilters.add(fgQ);
+    for (FacetContext ctx = fcontext; ctx != null; ctx = ctx.parent) {
+      if (null != ctx.filter) {
+        fgFilters.add(ctx.filter);
+      } else {
+        // sanity check...
+        // the only way the filter on the current context should be null is...
+        assert (// 1) it's the actual top most context,
+                //    (ie: the func is directly used w/o being nested under a facet)
+                (null == ctx.parent && fcontext == ctx) ||
+                // 2) it's a child of the top most context
+                //    (ie: the context of a top level facet)
+                (null == ctx.parent.parent && null == ctx.parent.filter));
+        // either way, no reason to keep looping up the (0 or 1) remaining ancestors
+        // (which is why #1 can assert '&& fcontext == ctx')
+        break;
+      }
+    }
+    
+    return new SKGSlotAcc(fcontext, numSlots, fgFilters, bgQ);
+  }
+
+  @Override
+  public FacetMerger createFacetMerger(Object prototype) {
+    return new Merger();
+  }
+  
+  private static final class SKGSlotAcc extends SlotAcc {
+    private BucketData[] slotvalues;
+    private final DocSet fgSet;
+    private final DocSet bgSet;
+    private final long fgSize;
+    private final long bgSize;
+    private final List<Query> fgFilters;
+    private final Query bgQ;
+    public SKGSlotAcc(FacetContext fcontext, int numSlots,
+                      List<Query> fgFilters, Query bgQ) throws IOException {
+      super(fcontext);
+      this.fgFilters = fgFilters;
+      this.bgQ = bgQ;
+      this.fgSet = fcontext.searcher.getDocSet(fgFilters);
+      this.bgSet = fcontext.searcher.getDocSet(bgQ);
+      // cache the set sizes for frequent re-use on every slot
+      this.fgSize = fgSet.size();
+      this.bgSize = bgSet.size();
+      this.slotvalues = new BucketData[numSlots];
+      reset();
+    }
+
+    private void processSlot(int slot, IntFunction<SlotContext> slotContext) throws IOException {
+      
+      assert null != slotContext;
+      
+      Query slotQ = slotContext.apply(slot).getSlotQuery();
+      if (null == slotQ) {
+        // extremeley special edge case...
+        // the only way this should be possible is if our skg() function is used as a "top level" stat
+        // w/o being nested under any facet, in which case it should be a FacetQuery w/no parent...
+        assert fcontext.processor.freq instanceof FacetQuery : fcontext.processor.freq;
+        assert null == fcontext.parent;
+        assert null == fcontext.filter;
+      }
+      // ...and in which case we should just use the current base
+      final DocSet slotSet = null == slotQ ? fcontext.base : fcontext.searcher.getDocSet(slotQ);
+
+      final BucketData slotVal = new BucketData();
+      slotVal.incSizes(fgSize, bgSize);
+      slotVal.incCounts(fgSet.intersectionSize(slotSet),
+                        bgSet.intersectionSize(slotSet));
+      slotvalues[slot] = slotVal;
+    }
+    
+    @Override
+    public void collect(int perSegDocId, int slot, IntFunction<SlotContext> slotContext) throws IOException {
+      // NOTE: we don't actaully care about the individual docs being collected
+      // (the only reason we even bother implementing this method is because it's needed for sorting
+      // buckets by a function)
+      
+      // so we only worry about ensuring that every "slot" / bucket is processed the first time
+      // we're asked about it...
+      if (null == slotvalues[slot]) {
+        processSlot(slot, slotContext);
+      }
+    }
+
+    @Override
+    public int collect(DocSet docs, int slot, IntFunction<SlotContext> slotContext) throws IOException {
+      // NOTE: we don't actaully care about the doc set being collected for the bucket
+      // so we only worry about ensuring that every "slot" / bucket is processed exactly once
+      
+      // if we're doing bulk collection, we better not be getting asked to re-use slots
+      assert null == slotvalues[slot];
+      processSlot(slot, slotContext);
+
+      // we don't do any filtering, we collect the whole docset, so return that as out collected count
+      // (as a stat, we're actually required to return this by assertions in FacetFieldProcessor.processStats)
+      return docs.size();
+    }
+
+    public int compare(int slotA, int slotB) {
+      final BucketData a = slotvalues[slotA];
+      final BucketData b = slotvalues[slotB];
+      
+      // we initialize & reset() (unused) slotvalues elements to null
+      // but we should never be asked to compare a slot that hasn't been collected...
+      assert null != a;
+      assert null != b;
+      return a.compareTo(b);
+    }
+
+    @Override
+    public Object getValue(int slotNum) {
+      BucketData slotVal = slotvalues[slotNum];
+      if (null == slotVal) {
+        // since we haven't been told about any docs for this slot, use a slot w/no counts,
+        // just the known fg/bg sizes. (this is most likely a refinement request for a bucket we dont have)
+        slotVal = new BucketData();
+        slotVal.incSizes(fgSize, bgSize);
+      }
+
+      SimpleOrderedMap res = slotVal.externalize(fcontext.isShard());
+      return res;
+    }
+
+    @Override
+    public void reset() {
+      Arrays.fill(slotvalues, null);
+    }
+
+    @Override
+    public void resize(Resizer resizer) {
+      slotvalues = resizer.resize(slotvalues, null);
+    }
+
+    @Override
+    public void close() throws IOException {
+      slotvalues = null;
+    }
+  }
+  
+  /**
+   * Encapsulates all data needed for a single bucket/slot
+   * 
+   * @see SKGSlotAcc
+   * @see Merger
+   */
+  private static final class BucketData implements Comparable<BucketData> {
+    
+    private long fg_size = 0;
+    private long bg_size = 0;
+    private long fg_count = 0;
+    private long bg_count = 0;
+    private double relatedness = Double.NaN;
+    
+    public BucketData() {
+      /* No-Op */
+    }
+
+    /** 
+     * Increment both the foreground &amp; background <em>counts</em> for the current bucket, reseting any
+     * derived values that may be cached
+     */
+    public void incCounts(final long fgInc, final long bgInc) {
+        this.relatedness = Double.NaN;
+        fg_count += fgInc;
+        bg_count += bgInc;
+    }
+    /** 
+     * Increment both the foreground &amp; background <em>sizes</em> for the current bucket, reseting any
+     * derived values that may be cached
+     */
+    public void incSizes(final long fgInc, final long bgInc) {
+        this.relatedness = Double.NaN;
+        fg_size += fgInc;
+        bg_size += bgInc;
+    }
+    
+    @Override
+    public int hashCode() {
+      return Objects.hash(this.getClass(), fg_count, bg_count, fg_size, bg_size);
+    }
+    
+    @Override
+    public boolean equals(Object other) {
+      if (!Objects.equals(this.getClass(), other.getClass())) {
+        return false;
+      }
+      BucketData that = (BucketData)other;
+      // we will most certainly be compared to other buckets of the same Agg instance, so compare counts first
+      return Objects.equals(this.fg_count, that.fg_count)
+        && Objects.equals(this.bg_count, that.bg_count)
+        && Objects.equals(this.fg_size, that.fg_size)
+        && Objects.equals(this.bg_size, that.bg_size);
+    }
+
+    /**
+     * Computes (and caches) the derived relatedness score for this bucket
+     */
+    private double getRelatedness() {
+      if (Double.isNaN(this.relatedness)) {
+        this.relatedness = computeRelatedness(this.fg_count, this.fg_size,
+                                              this.bg_count, this.bg_size);
+        // TODO: add support for a "min_pop" option...
+        //
+        // if min_pop is configured, and either (fg|bg) popularity is lower then that value
+        // then "this.relatedness=-Infinity" so it sorts at the bottom
+        // this logic be ignored on isShard requests -- similar to how shards ignore 'mincount'
+      }
+      return this.relatedness;
+    }
+    
+    @Override
+    public int compareTo(BucketData that) {
+      // TODO: add support for a "sort_val" option...
+      //
+      // default should be "relatedness" but also support "foreground" and "background" ...
+      // either of those should sort by the corrisponding ratio
+      // To do this, we should probably precommpute the ratios in incCounts
+      
+      int r = Double.compare(this.getRelatedness(), that.getRelatedness());
+      if (0 == r) {
+        r = Long.compare(this.fg_count, that.fg_count);
+      }
+      if (0 == r) {
+        r = Long.compare(this.bg_count, that.bg_count);
+      }
+      return r;
+    }
+    
+    /**
+     * @see SlotAcc#getValue
+     * @see Merger#getMergedResult
+     */
+    public SimpleOrderedMap externalize(final boolean isShardRequest) {
+      SimpleOrderedMap result = new SimpleOrderedMap<Number>();
+      
+      if (isShardRequest) {
+        result.add(FG_COUNT, fg_count);
+        result.add(BG_COUNT, bg_count);
+        // NOTE: sizes will be the same for every slot...
+        // TODO: it would be nice to put them directly in the parent facet, instead of every bucket,
+        // in order to reduce the size of the response.
+        result.add(FG_SIZE, fg_size); 
+        result.add(BG_SIZE, bg_size);
+      } else {
+        // there's no need to bother computing these when returning results *to* a shard coordinator
+        // only useful to external clients 
+        result.add(RELATEDNESS, this.getRelatedness());
+        result.add(FG_POP, roundTo5Digits((double) fg_count / bg_size)); // yes, BACKGROUND size is intentional
+        result.add(BG_POP, roundTo5Digits((double) bg_count / bg_size));
+      }
+      
+      return result;
+    }
+  }
+
+  /**
+   * Merges in the per shard {@link BucketData} output into a unified {@link BucketData}
+   */
+  private static final class Merger extends FacetSortableMerger {
+    private final BucketData mergedData = new BucketData();
+    
+    @Override
+    public void merge(Object facetResult, Context mcontext) {
+      NamedList<Object> shardData = (NamedList<Object>)facetResult;
+      mergedData.incSizes((Long)shardData.remove(FG_SIZE), (Long)shardData.remove(BG_SIZE));
+      mergedData.incCounts((Long)shardData.remove(FG_COUNT), (Long)shardData.remove(BG_COUNT));
+    }
+
+    @Override
+    public int compareTo(FacetSortableMerger other, FacetRequest.SortDirection direction) {
+      // NOTE: regardless of the SortDirection hint, we want normal comparison of the BucketData
+      
+      assert other instanceof Merger;
+      Merger that = (Merger)other;
+      return mergedData.compareTo(that.mergedData);
+    }
+    
+    @Override
+    public Object getMergedResult() {
+      return mergedData.externalize(false);
+    }
+  }
+
+  
+  /**
+   * This is an aproximated Z-Score, as described in the "Scoring Semantic Relationships" 
+   * section of "<a href="https://arxiv.org/pdf/1609.00464.pdf">The Semantic Knowledge Graph: 
+   * A compact, auto-generated model for real-time traversal and ranking of any relationship 
+   * within a domain</a>"
+   *
+   * See Also:<ul>
+   * <li><a href="https://s.apache.org/Mfu2">java-user@lucene Message-ID: 449AEB60.4070300@alias-i.com</a></li>
+   * <li><a href="https://lingpipe-blog.com/2006/03/29/interesting-phrase-extraction-binomial-hypothesis-testing-vs-coding-loss/">Phrase Extraction: Binomial Hypothesis Testing vs. Coding Loss</a></li>
+   * </ul>
+   */
+  // NOTE: javadoc linter freaks out if we try doing those links as '@see <a href=...' tags
+  public static double computeRelatedness(final long fg_count, final long fg_size,
+                                          final long bg_count, final long bg_size) {
+    final double fg_size_d = (double) fg_size;
+    final double bg_size_d = (double) bg_size;
+    final double bg_prob = (bg_count / bg_size_d);
+    final double num = fg_count - fg_size_d * bg_prob;
+    double denom = Math.sqrt(fg_size_d * bg_prob * (1 - bg_prob));
+    denom = (denom == 0) ? 1e-10 : denom;
+    final double z = num / denom;
+    final double result = 0.2 * sigmoidHelper(z, -80, 50)
+      + 0.2 * sigmoidHelper(z, -30, 30)
+      + 0.2 * sigmoidHelper(z, 0, 30)
+      + 0.2 * sigmoidHelper(z, 30, 30)
+      + 0.2 * sigmoidHelper(z, 80, 50);
+    return roundTo5Digits(result);
+    
+  }
+  /**
+   * Helper function for rounding/truncating relatedness &amp; popularity values to 
+   * 5 decimal digits, since these values are all probabilistic more then 5 digits aren't really relevant
+   * and may give a missleading impression of added precision.
+   */
+  public static double roundTo5Digits(final double val) {
+    return Math.round(val * 1e5) / 1e5;
+  }
+  
+  /** A helper function for scaling values */
+  private static double sigmoidHelper(final double x, final double offset, final double scale) {
+    return (x+offset) / (scale + Math.abs(x+offset));
+  }
+}
+

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/SlotAcc.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/SlotAcc.java b/solr/core/src/java/org/apache/solr/search/facet/SlotAcc.java
index 9165799..9c12aff 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/SlotAcc.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/SlotAcc.java
@@ -23,11 +23,13 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.queries.function.FunctionValues;
 import org.apache.lucene.queries.function.ValueSource;
 import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.search.Query;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.solr.common.util.SimpleOrderedMap;
 import org.apache.solr.search.DocIterator;
@@ -65,9 +67,45 @@ public abstract class SlotAcc implements Closeable {
     }
   }
 
-  public abstract void collect(int doc, int slot) throws IOException;
+  /**
+   * @deprecated This method exists only for backcompatibility, developers of new {@link SlotAcc} 
+   * implementations should not implement this method, and should instead override 
+   * {@link #collect(int,int,IntFunction)}
+   */
+  @Deprecated
+  public void collect(int doc, int slot) throws IOException {
+    throw new UnsupportedOperationException
+      ("SlotAcc implementations must implement 'collect(int,int,IntFunction<SlotContext>)' or the (deprecated)"
+      + "'collect(int,int)'");
+  }
+  
+  /**
+   * All subclasses should override this method, for backcompatability the default implementaion
+   * delegates to the (deprecated) {@link #collect(int,int)}
+   *
+   * @param doc Single Segment docId (relative to the current {@link LeafReaderContext} to collect
+   * @param slot The slot number to collect this document in
+   * @param slotContext A callback that can be used for Accumulators that would like additional info 
+   *        about the current slot -- the {@link IntFunction} is only garunteed to be valid for 
+   *        the current slot, and the {@link SlotContext} returned is only valid for the duration 
+   *        of the <code>collect()</code> call.
+   */
+  @Deprecated
+  public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
+    collect(doc,slot);
+  }
 
-  public int collect(DocSet docs, int slot) throws IOException {
+  /**
+   * Bulk collection of all documents in a slot.  The default implementation calls {@link #collect(int,int,IntFunction)}
+   *
+   * @param docs (global) Documents to collect
+   * @param slot The slot number to collect these documents in
+   * @param slotContext A callback that can be used for Accumulators that would like additional info 
+   *        about the current slot -- the {@link IntFunction} is only garunteed to be valid for 
+   *        the current slot, and the {@link SlotContext} returned is only valid for the duration 
+   *        of the <code>collect()</code> call.
+   */
+  public int collect(DocSet docs, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     int count = 0;
     SolrIndexSearcher searcher = fcontext.searcher;
 
@@ -94,7 +132,7 @@ public abstract class SlotAcc implements Closeable {
         setNextReader(ctx);
       }
       count++;
-      collect(doc - segBase, slot); // per-seg collectors
+      collect(doc - segBase, slot, slotContext); // per-seg collectors
     }
     return count;
   }
@@ -212,6 +250,19 @@ public abstract class SlotAcc implements Closeable {
 
   } // end class Resizer
 
+  /**
+   * Incapsulates information about the current slot, for Accumulators that may want 
+   * additional info during collection.
+   */
+  public static final class SlotContext {
+    private final Query slotQuery;
+    public SlotContext(Query slotQuery) {
+      this.slotQuery = slotQuery;
+    }
+    public Query getSlotQuery() {
+      return slotQuery;
+    }
+  }
 }
 
 // TODO: we should really have a decoupled value provider...
@@ -349,7 +400,7 @@ class SumSlotAcc extends DoubleFuncSlotAcc {
     super(values, fcontext, numSlots);
   }
 
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     double val = values.doubleVal(doc); // todo: worth trying to share this value across multiple stats that need it?
     result[slotNum] += val;
   }
@@ -361,7 +412,7 @@ class SumsqSlotAcc extends DoubleFuncSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     double val = values.doubleVal(doc);
     val = val * val;
     result[slotNum] += val;
@@ -386,7 +437,7 @@ class AvgSlotAcc extends DoubleFuncSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     double val = values.doubleVal(doc);
     if (val != 0 || values.exists(doc)) {
       result[slotNum] += val;
@@ -479,7 +530,7 @@ class VarianceSlotAcc extends DoubleFuncSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slot) throws IOException {
+  public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     double val = values.doubleVal(doc);
     if (values.exists(doc)) {
       counts[slot]++;
@@ -541,7 +592,7 @@ class StddevSlotAcc extends DoubleFuncSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slot) throws IOException {
+  public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     double val = values.doubleVal(doc);
     if (values.exists(doc)) {
       counts[slot]++;
@@ -570,8 +621,9 @@ class CountSlotArrAcc extends CountSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slotNum) { // TODO: count arrays can use fewer bytes based on the number of docs in
-                                              // the base set (that's the upper bound for single valued) - look at ttf?
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) {
+    // TODO: count arrays can use fewer bytes based on the number of docs in
+    // the base set (that's the upper bound for single valued) - look at ttf?
     result[slotNum]++;
   }
 
@@ -615,7 +667,7 @@ class SortSlotAcc extends SlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slot) throws IOException {
+  public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
     // no-op
   }
 

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/UnInvertedField.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/UnInvertedField.java b/solr/core/src/java/org/apache/solr/search/facet/UnInvertedField.java
index 69b341a..3349bb2 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/UnInvertedField.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/UnInvertedField.java
@@ -44,6 +44,7 @@ import org.apache.solr.search.DocIterator;
 import org.apache.solr.search.DocSet;
 import org.apache.solr.search.SolrCache;
 import org.apache.solr.search.SolrIndexSearcher;
+import org.apache.solr.search.facet.SlotAcc.SlotContext;
 import org.apache.solr.uninverting.DocTermOrds;
 import org.apache.solr.util.TestInjection;
 import org.slf4j.Logger;
@@ -431,7 +432,8 @@ public class UnInvertedField extends DocTermOrds {
       if (tt.termNum >= startTermIndex && tt.termNum < endTermIndex) {
         // handle the biggest terms
         DocSet intersection = searcher.getDocSet(tt.termQuery, docs);
-        int collected = processor.collectFirstPhase(intersection, tt.termNum - startTermIndex);
+        int collected = processor.collectFirstPhase(intersection, tt.termNum - startTermIndex,
+                                                    slotNum -> { return new SlotContext(tt.termQuery); });
         countAcc.incrementCount(tt.termNum - startTermIndex, collected);
         if (collected > 0) {
           uniqueTerms++;
@@ -493,7 +495,7 @@ public class UnInvertedField extends DocTermOrds {
             if (arrIdx < 0) continue;
             if (arrIdx >= nTerms) break;
             countAcc.incrementCount(arrIdx, 1);
-            processor.collectFirstPhase(segDoc, arrIdx);
+            processor.collectFirstPhase(segDoc, arrIdx, processor.slotContext);
           }
         } else {
           int tnum = 0;
@@ -507,7 +509,7 @@ public class UnInvertedField extends DocTermOrds {
               if (arrIdx >= 0) {
                 if (arrIdx >= nTerms) break;
                 countAcc.incrementCount(arrIdx, 1);
-                processor.collectFirstPhase(segDoc, arrIdx);
+                processor.collectFirstPhase(segDoc, arrIdx, processor.slotContext);
               }
               delta = 0;
             }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/UniqueAgg.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/UniqueAgg.java b/solr/core/src/java/org/apache/solr/search/facet/UniqueAgg.java
index d858b5b..5d9cf90 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/UniqueAgg.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/UniqueAgg.java
@@ -21,6 +21,7 @@ import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.LeafReaderContext;
@@ -145,7 +146,7 @@ public class UniqueAgg extends StrAggValueSource {
     }
 
     @Override
-    public void collect(int doc, int slot) throws IOException {
+    public void collect(int doc, int slot, IntFunction<SlotContext> slotContext) throws IOException {
       int valuesDocID = docIdSetIterator().docID();
       if (valuesDocID < doc) {
         valuesDocID = docIdSetIterator().advance(doc);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java b/solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java
index af419a4..839fc52 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java
@@ -18,6 +18,7 @@
 package org.apache.solr.search.facet;
 
 import java.io.IOException;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiDocValues;
@@ -70,7 +71,7 @@ class UniqueMultiDvSlotAcc extends UniqueSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     if (subDv.advanceExact(doc)) {
 
       int segOrd = (int) subDv.nextOrd();

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java b/solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java
index 10adcf0..508da38 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java
@@ -18,6 +18,7 @@
 package org.apache.solr.search.facet;
 
 import java.io.IOException;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FixedBitSet;
@@ -50,7 +51,7 @@ class UniqueMultivaluedSlotAcc extends UniqueSlotAcc implements UnInvertedField.
   }
 
   @Override
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     bits = arr[slotNum];
     if (bits == null) {
       bits = new FixedBitSet(nTerms);
@@ -67,4 +68,4 @@ class UniqueMultivaluedSlotAcc extends UniqueSlotAcc implements UnInvertedField.
       docToTerm = null;
     }
   }
-}
\ No newline at end of file
+}

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/669b9e7a/solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java
----------------------------------------------------------------------
diff --git a/solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java b/solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java
index 9a1b51e..ed51c5b 100644
--- a/solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java
+++ b/solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java
@@ -18,6 +18,7 @@
 package org.apache.solr.search.facet;
 
 import java.io.IOException;
+import java.util.function.IntFunction;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiDocValues;
@@ -73,7 +74,7 @@ class UniqueSinglevaluedSlotAcc extends UniqueSlotAcc {
   }
 
   @Override
-  public void collect(int doc, int slotNum) throws IOException {
+  public void collect(int doc, int slotNum, IntFunction<SlotContext> slotContext) throws IOException {
     if (doc > subDv.docID()) {
       subDv.advance(doc);
     }