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Posted to commits@marmotta.apache.org by ja...@apache.org on 2013/11/05 11:52:25 UTC

[20/52] [partial] Reverting the erroneous merge by Sebastian according to the instructions in INFRA-6876

http://git-wip-us.apache.org/repos/asf/incubator-marmotta/blob/582abb5b/libraries/kiwi/kiwi-sparql/src/main/java/org/apache/marmotta/kiwi/sparql/sqlmapper/SparqlToSQLMapper.java
----------------------------------------------------------------------
diff --git a/libraries/kiwi/kiwi-sparql/src/main/java/org/apache/marmotta/kiwi/sparql/sqlmapper/SparqlToSQLMapper.java b/libraries/kiwi/kiwi-sparql/src/main/java/org/apache/marmotta/kiwi/sparql/sqlmapper/SparqlToSQLMapper.java
deleted file mode 100644
index 8bf0677..0000000
--- a/libraries/kiwi/kiwi-sparql/src/main/java/org/apache/marmotta/kiwi/sparql/sqlmapper/SparqlToSQLMapper.java
+++ /dev/null
@@ -1,2427 +0,0 @@
-/**
- * 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.marmotta.platform.sparql.services.evaluation.sql;
-
-import org.apache.marmotta.platform.sparql.model.Tables;
-import org.apache.marmotta.platform.sparql.model.tables.TNodes;
-import org.apache.marmotta.platform.sparql.model.tables.TTriples;
-import org.apache.marmotta.platform.sparql.model.tables.records.RNodes;
-import org.apache.marmotta.commons.sesame.model.Namespaces;
-import org.apache.marmotta.commons.util.DateUtils;
-import at.newmedialab.sesame.commons.util.HashUtils;
-import com.google.common.collect.Sets;
-import org.apache.marmotta.platform.core.api.config.ConfigurationService;
-import org.apache.marmotta.platform.core.api.triplestore.ResourceService;
-import org.apache.marmotta.platform.core.model.rdf.KiWiNode;
-import org.apache.marmotta.platform.core.model.rdf.KiWiUriResource;
-import org.apache.marmotta.platform.core.util.KiWiContext;
-import org.jooq.*;
-import org.jooq.conf.RenderNameStyle;
-import org.jooq.conf.StatementType;
-import org.jooq.impl.Factory;
-import org.jooq.impl.SQLDataType;
-import org.openrdf.model.BNode;
-import org.openrdf.model.Literal;
-import org.openrdf.model.URI;
-import org.openrdf.model.Value;
-import org.openrdf.model.impl.CalendarLiteralImpl;
-import org.openrdf.model.impl.DecimalLiteralImpl;
-import org.openrdf.model.impl.IntegerLiteralImpl;
-import org.openrdf.query.algebra.*;
-import org.openrdf.query.algebra.helpers.QueryModelVisitorBase;
-import org.openrdf.query.parser.sparql.ast.VisitorException;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import java.sql.Connection;
-import java.sql.Timestamp;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-
-/**
- * A class implementing the query model visitor to translate a SPARQL algebra model to a SQL query using the JOOQ
- * Java to SQL mapper. Takes a JDBC database connection and a SQLDialect as argument, based on which the
- * translation takes place. The resulting SQL query can be retrieved by calling the getQuery() method.
- * <p/>
- * The SPARQL->SQL mapper translates the major SPARQL constructs as follows:
- * <ul>
- *     <li>a triple pattern is translated into a join of the TRIPLES table with the subject,
- *         property, object, and optionally context nodes; each variable occurring in the pattern
- *         represents a separate query to the KIWINODES table; variables with the same name
- *         are reused to ensure SPARQL joins to be translated into SQL JOINs</li>
- *     <li>a JOIN between triple patterns is translated into an SQL INNER JOIN, using the variables used
- *         in the triple patterns as JOIN conditions</li>
- *     <li>an OPTIONAL between triple patterns is translated into an SQL LEFT OUTER JOIN, using the
- *         variables occurring in the optional pattern as join conditions</li>
- *     <li>a UNION is translated into an SQL UNION; since SPARQL untions occur inside
- *         the WHERE part of the query, the UnionOptimizer moves them out to the top level
- *         so the UNION is always calculated properly over SQL queries</li>
- *     <li>INTERSECTION and DIFFERENCE are translated similar to UNION queries to INTERSECTION and EXCEPT
- *         in SQL</li>
- *     <li>variables are named queries to the KIWINODES table; in case the value of a variable is
- *         needed, the getValue() method below translates the table representation into either the
- *         content, uri, or anonId fields of the table; in case the variable is returned by the
- *         projection, the mapping translates it into the ID field of the table to be able to
- *         load the complete RDF node; specialised methods are implemented for accessing the
- *         double, integer, or date content of a variable</li>
- *     <li>SPARQL functions and operators are translated as far as possible directly into their
- *         SQL counterparts; for constructs where a SQL equivalent does not exist, an exception
- *         is thrown</li>
- * </ul>
- * <p/>
- * Author: Sebastian Schaffert
- */
-public class SparqlToSQLMapper  {
-
-    private static Logger log = LoggerFactory.getLogger(SparqlToSQLMapper.class);
-
-    // TODO: implement language tag matches using this regular expression
-    static final String langtag_ex =
-            "(\\A[xX]([\\x2d]\\p{Alnum}{1,8})*\\z)"
-                    + "|(((\\A\\p{Alpha}{2,8}(?=\\x2d|\\z)){1}"
-                    + "(([\\x2d]\\p{Alpha}{3})(?=\\x2d|\\z)){0,3}"
-                    + "([\\x2d]\\p{Alpha}{4}(?=\\x2d|\\z))?"
-                    + "([\\x2d](\\p{Alpha}{2}|\\d{3})(?=\\x2d|\\z))?"
-                    + "([\\x2d](\\d\\p{Alnum}{3}|\\p{Alnum}{5,8})(?=\\x2d|\\z))*)"
-                    + "(([\\x2d]([a-wyzA-WYZ](?=\\x2d))([\\x2d](\\p{Alnum}{2,8})+)*))*"
-                    + "([\\x2d][xX]([\\x2d]\\p{Alnum}{1,8})*)?)\\z";
-
-
-    private Factory create;
-
-    /** jOOQ representation of the triples table */
-    private TTriples T_TRIPLES;
-
-    /** jOOQ representation of the nodes table */
-    private TNodes T_NODES;
-
-    /** jOOQ representation of the namespaces table */
-    private Table<Record> T_NAMESPACES;
-
-
-    private SQLDialect dialect;
-
-    // keep track of the variables that have so far been used in the query;
-    // currentVariables is used by sub queries
-    private Map<String,TNodes> variables;
-    private Map<String,TNodes> currentVariables;
-
-    // map from URI resources to nodes table, to avoid unnecessary joins
-    private Map<String,TNodes> uriNodes;
-
-
-    // keep track of SPARQL extension values used in the query; extension values are bound e.g. to
-    // function results
-    private Map<String,Field> extensions;
-
-    // count current triple; used for naming triple patterns
-    private int tripleCounter = 0;
-
-    // the set of variables that are actually projected by this query
-    private Set<String> projectedVariables;
-
-    // the set of extensions that are projected by this query (together with type information for proper casting)
-    private HashMap<String,Class> extensionVariables;
-
-
-    // collect mappings from internal variable name to result variable name; filled by Projection
-    private Map<String,String> variableMappings;
-    private Map<String,String> revVariableMappings;
-
-    // fields used for sorting the results
-    private Map<String,Field> sortFields;
-    private Map<String,Set<String>> sortDependencies;
-
-
-    // store variables that can only be used as resources; for such variables, we can detect the getValue
-    // method, because in this case we only need to return the URI as string value
-    private Set<String> resourceVariables;
-
-    private Select query;
-
-    private CastType typeCast;
-
-    // collection of fields on which to group the query; collected by group(), used by projection() ...
-    private Set<String> groupBy;
-
-    private ResourceService resourceService;
-
-    private ConfigurationService configurationService;
-
-    public SparqlToSQLMapper(Connection connection, SQLDialect dialect, CastType typeCast) {
-        create = new Factory(connection,dialect);
-        create.getSettings().setRenderFormatted(true);
-        create.getSettings().setRenderNameStyle(RenderNameStyle.LOWER);
-        create.getSettings().setStatementType(StatementType.STATIC_STATEMENT);
-
-        this.dialect = dialect;
-
-        T_TRIPLES    = Tables.TRIPLES;
-        T_NODES      = Tables.KIWINODE;
-        T_NAMESPACES = create.table("KIWINAMESPACE");
-
-        variables = new HashMap<String, TNodes>();
-        currentVariables = new HashMap<String, TNodes>();
-        projectedVariables = new HashSet<String>();
-        extensionVariables = new HashMap<String, Class>();
-
-        extensions = new HashMap<String, Field>();
-
-        variableMappings = new HashMap<String, String>();
-        revVariableMappings = new HashMap<String, String>();
-        sortFields = new HashMap<String, Field>();
-        sortDependencies = new HashMap<String, Set<String>>();
-
-        resourceVariables = new HashSet<String>();
-
-        uriNodes = new HashMap<String, TNodes>();
-
-        groupBy = new HashSet<String>();
-
-        this.typeCast = typeCast;
-
-        // require some beans to get additional information
-        this.resourceService = KiWiContext.getInstance(ResourceService.class);
-        this.configurationService = KiWiContext.getInstance(ConfigurationService.class);
-    }
-
-    public SparqlToSQLMapper(Connection connection, SQLDialect dialect, TupleExpr queryRoot, CastType typeCast) {
-        this(connection,dialect, typeCast);
-
-        query = meetTupleExpression(queryRoot, create.selectQuery(), new HashSet<Condition>(), new HashSet<String>());
-    }
-
-    public SparqlToSQLMapper(Connection connection, SQLDialect dialect, ValueExpr queryRoot, CastType typeCast) {
-        this(connection,dialect, typeCast);
-
-        query = create.select((Field)meetValueExpression(queryRoot));
-    }
-
-
-
-    public Select getQuery() {
-        return query;
-    }
-
-
-    public Set<String> getProjectedVariables() {
-        return projectedVariables;
-    }
-
-    public HashMap<String, Class> getExtensionVariables() {
-        return extensionVariables;
-    }
-
-    public Condition meet(And node)  {
-        QueryPart leftPart = meetValueExpression(node.getLeftArg());
-        QueryPart rightPart = meetValueExpression(node.getRightArg());
-
-        if(! (leftPart instanceof Condition) || !(rightPart instanceof Condition)) {
-            throw new IllegalStateException("the left or right part of the AND condition are not boolean: "+node);
-        }
-
-        return ((Condition)leftPart).and((Condition)rightPart);
-
-    }
-
-
-    public SelectQuery arbitraryLengthPath(ArbitraryLengthPath node, SelectQuery query)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public Field avg(Avg node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-
-        return getDoubleValue(part, true).avg();
-    }
-
-
-    public SelectQuery bindingSetAssignment(BindingSetAssignment node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-
-    public QueryPart bound(Bound node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        // variable
-        if(part instanceof TNodes) {
-            return create.condition(part + ".id is not null") ;
-        } else {
-            throw new IllegalArgumentException("NOT NULL can only be computed for the node table; type was: "+part.getClass().getName());
-        }
-    }
-
-
-
-    public Field coalesce(Coalesce node)  {
-
-        /*
-        if(node.getArguments().size() > 0) {
-            Field part1;
-            Field[] parts2_n = new Field[node.getArguments().size()-1];
-            for(int i=0; i<node.getArguments().size(); i++) {
-                QueryPart part = meetValueExpression(node.getArguments().get(i));
-                if(part instanceof Table && ((Table) part).getName().equals(T_NODES.getName())) {
-                    if(i == 0) {
-                        part1 = ((Table)part).getField("");
-                    } else {
-                        parts2_n[i-1] = (Table)part;
-                    }
-                } else {
-                    throw new IllegalArgumentException("COALESCE can only be computed for the node table; type was: "+part.getClass().getName());
-                }
-
-            }
-            return create.coalesce()
-        }
-        */
-
-
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public Condition compare(Compare node)  {
-        QueryPart leftArg = meetValueExpression(node.getLeftArg());
-        QueryPart rightArg = meetValueExpression(node.getRightArg());
-
-        Field left, right;
-
-        // type negotiation:
-        // 1. if both are variables, casting should take place based on the type field, or if no type is given, we use
-        // the value returned by getValue (might be the URI)
-        if(leftArg instanceof TNodes && rightArg instanceof TNodes) {
-            TNodes tleft  = (TNodes) leftArg;
-            TNodes tright = (TNodes) rightArg;
-
-            switch (node.getOperator()) {
-                case EQ:
-                    return create.decode().when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.equal(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.equal(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.equal(tright.CONTENT))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.equal(tright.DATECONTENT))
-                            .when(tleft.NODETYPE.equal("URI").and(tright.NODETYPE.equal("URI")),tleft.URI.equal(tright.URI))
-                            .when(tleft.NODETYPE.equal("ANON").and(tright.NODETYPE.equal("ANON")),tleft.ID.equal(tright.ID))
-                            .otherwise(create.falseCondition()).isTrue();
-                case GE:
-                    return create.decode().when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.greaterOrEqual(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.greaterOrEqual(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.greaterOrEqual(tright.DATECONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.greaterOrEqual(tright.CONTENT))
-                            .otherwise(create.falseCondition()).isTrue();
-                case GT:
-                    return create.decode().when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.greaterThan(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.greaterThan(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.greaterThan(tright.CONTENT))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.greaterThan(tright.DATECONTENT))
-                            .otherwise(create.falseCondition()).isTrue();
-                case LE:
-                    return create.decode().when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.lessOrEqual(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.lessOrEqual(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.lessOrEqual(tright.CONTENT))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.lessOrEqual(tright.DATECONTENT))
-                            .otherwise(create.falseCondition()).isTrue();
-                case LT:
-                    return create.decode().when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.lessThan(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.lessThan(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.lessThan(tright.CONTENT))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.lessThan(tright.DATECONTENT))
-                            .otherwise(create.falseCondition()).isTrue();
-                case NE:
-                    return create.decode()  .when(tleft.NODETYPE.equal("DOUBLE").and(tright.NODETYPE.equal("DOUBLE")), tleft.DOUBLECONTENT.notEqual(tright.DOUBLECONTENT))
-                            .when(tleft.NODETYPE.equal("INTEGER").and(tright.NODETYPE.equal("INTEGER")), tleft.INTCONTENT.notEqual(tright.INTCONTENT))
-                            .when(tleft.NODETYPE.equal("STRING").and(tright.NODETYPE.equal("STRING")),tleft.CONTENT.notEqual(tright.CONTENT))
-                            .when(tleft.NODETYPE.equal("URI").and(tright.NODETYPE.equal("URI")),tleft.URI.notEqual(tright.URI))
-                            .when(tleft.NODETYPE.equal("ANON").and(tright.NODETYPE.equal("ANON")),tleft.ID.notEqual(tright.ID))
-                            .when(tleft.NODETYPE.equal("DATE").and(tright.NODETYPE.equal("DATE")),tleft.DATECONTENT.notEqual(tright.DATECONTENT))
-                            .otherwise(create.falseCondition()).isTrue();
-
-            }
-
-            throw new IllegalArgumentException("unknown operator for comparison: "+node.getOperator());
-
-            // 2. if only one is a variable, we take the type of the other argument and cast the variable to either string or
-            // double for comparison
-        } else if(leftArg instanceof TNodes && rightArg instanceof Field) {
-            if(((Field) rightArg).getType().equals(Long.class)) {
-                left = getIntegerValue(leftArg, typeCast == CastType.STRICT);
-                right = getIntegerValue(rightArg, typeCast == CastType.STRICT);
-            } else if(((Field) rightArg).getType().equals(Double.class)) {
-                left = getDoubleValue(leftArg, typeCast == CastType.STRICT);
-                right = getDoubleValue(rightArg, typeCast == CastType.STRICT);
-            } else if(((Field) rightArg).getType().equals(Timestamp.class)) {
-                left = getDateValue(leftArg, typeCast == CastType.STRICT);
-                right = getDateValue(rightArg, typeCast == CastType.STRICT);
-            } else {
-                left = getValue(leftArg, typeCast == CastType.STRICT);
-                right = getValue(rightArg, typeCast == CastType.STRICT);
-            }
-        } else if(rightArg instanceof TNodes && leftArg instanceof Field) {
-            if(((Field) leftArg).getType().equals(Long.class)) {
-                left = getIntegerValue(leftArg, typeCast == CastType.STRICT);
-                right = getIntegerValue(rightArg, typeCast == CastType.STRICT);
-            } else if(((Field) leftArg).getType().equals(Double.class)) {
-                left = getDoubleValue(leftArg, typeCast == CastType.STRICT);
-                right = getDoubleValue(rightArg, typeCast == CastType.STRICT);
-            } else if(((Field) leftArg).getType().equals(Timestamp.class)) {
-                left = getDateValue(leftArg, typeCast == CastType.STRICT);
-                right = getDateValue(rightArg, typeCast == CastType.STRICT);
-            } else {
-                left = getValue(leftArg, typeCast == CastType.STRICT);
-                right = getValue(rightArg, typeCast == CastType.STRICT);
-            }
-        } else {
-            left   = getValue(leftArg, true);
-            right  = getValue(rightArg, true);
-        }
-
-
-
-        // TODO: here we could possibly also work with getAlternativeValues, but it is unclear to me what comparison with null fields will yield!
-        // maybe we need sth like (x is not null AND x < y)
-
-
-        switch(node.getOperator()) {
-            case EQ:
-                return left.equal(right);
-            case GE:
-                return left.greaterOrEqual(right);
-            case GT:
-                return left.greaterThan(right);
-            case LE:
-                return left.lessOrEqual(right);
-            case LT:
-                return left.lessThan(right);
-            case NE:
-                return left.notEqual(right);
-        }
-
-        throw new IllegalArgumentException("unknown operator for comparison: "+node.getOperator());
-    }
-
-
-    public QueryPart compareAll(CompareAll node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public QueryPart compareAny(CompareAny node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-
-    public Field count(Count node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof TNodes) {
-            return ((TNodes)part).ID.count();
-
-        } else {
-            throw new IllegalArgumentException("COUNT is only supported for variables, was: "+part.getClass().getName());
-        }
-    }
-
-
-    public Field datatype(Datatype node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof TNodes) {
-            return ((TNodes)part).TYPE;
-
-        } else {
-            throw new IllegalArgumentException("DATATYPE is only supported for variables, was: "+part.getClass().getName());
-        }
-    }
-
-
-
-    public List<JoinTable> difference(Difference node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections,Collection<Table> tables)  {
-        return merge(node,query,MergeType.DIFFERENCE, conditions,  projections, tables);
-    }
-
-
-    public Select distinct(Distinct node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-
-        Select subQuery = meetTupleExpression(node.getArg(), query,  conditions,  projections);
-
-        if(subQuery instanceof SelectQuery) {
-            ((SelectQuery) subQuery).setDistinct(true);
-            return subQuery;
-        } else {
-            return create.selectDistinct().from(subQuery);
-        }
-
-        /*
-        try {
-            // distinct and order by is not possible in SQL
-            if(! (new HasOrderBy(node).isTrue())) {
-                query.setDistinct(true);
-                return meetTupleExpression(node.getArg(), query, type);
-            } else {
-                // we have to do a subquery first and then select the distinct values
-                Select subquery = meetTupleExpression(node.getArg(), query, type);
-
-                return create.selectDistinct().from(subquery);
-            }
-        } catch (VisitorException e) {
-            return meetTupleExpression(node.getArg(),query,type);
-        }
-        */
-    }
-
-
-    public SelectQuery emptySet(EmptySet node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        query.addConditions(create.falseCondition());
-        return query;
-    }
-
-
-    public Condition exists(Exists node)  {
-        // save previous state
-        Map<String,TNodes> oldVars = currentVariables;
-
-        currentVariables = new HashMap<String, TNodes>(oldVars);   // copy over old variable mappings so modifications have no influence to the rest of the evaluation
-        SelectQuery subQuery = create.selectQuery();
-        Set<Condition> conditions = new HashSet<Condition>();
-        List<Table> tables = new ArrayList<Table>();
-
-        Table from = null;
-        for(JoinTable tbl : meetTableLike(node.getSubQuery(),subQuery, conditions, new HashSet<String>(), tables)) {
-            if(from == null) {
-                from = tbl.getTable();
-                subQuery.addConditions(tbl.getConditions());
-            } else {
-                from = from.join(tbl.getTable()).on(tbl.getConditions().toArray(new Condition[0]));
-            }
-        }
-        subQuery.addFrom(from);
-        subQuery.addConditions(conditions);
-        if(tables.size() > 0 && tables.get(0) instanceof TTriples) {
-            subQuery.addSelect(((TTriples)tables.get(0)).ID.as("_singlevalue"));
-        }
-        subQuery.addLimit(1);
-
-        // reload previous state
-        currentVariables = oldVars;
-
-        return create.exists(subQuery);
-    }
-
-
-    public List<JoinTable> extension(Extension node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-        List<JoinTable> select;
-        if(node.getArg() instanceof SingletonSet) {
-            // TODO: optimization would be to not run against the database at all ...
-            select = new ArrayList<JoinTable>();
-        } else {
-            select = meetTableLike(node.getArg(), query, conditions, projections, tables);
-        }
-
-        for(ExtensionElem elem : node.getElements()) {
-            extensionElem(elem);
-        }
-
-        return select;
-    }
-
-    public void extensionElem(ExtensionElem elem) {
-        if(elem.getExpr() instanceof Var) {
-            // do nothing, declaration
-        } else {
-            extensions.put(elem.getName().replace("-","_"), getValue(meetValueExpression(elem.getExpr()), true));
-        }
-    }
-
-
-    public List<JoinTable> filter(Filter node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-        List<JoinTable> tableList = meetTableLike(node.getArg(), query, conditions, projections, tables); // ensure the tables are evaluated before the conditions
-
-        QueryPart condition = meetValueExpression(node.getCondition());
-        if(condition instanceof Condition) {
-            conditions.add((Condition)condition);
-        } else {
-            throw new IllegalStateException("the transformation of the value expression did not result in a Condition");
-        }
-
-
-
-        return tableList;
-    }
-
-
-    public QueryPart functionCall(FunctionCall node)  {
-        if(node.getURI().equals(Namespaces.NS_XSD+"double") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg, true);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"float") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg, true);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"decimal") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getIntegerValue(arg, true);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"integer") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getIntegerValue(arg, true);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"boolean") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getValue(arg, true).cast(SQLDataType.BOOLEAN);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"string") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getValue(arg, true);
-        } else if(node.getURI().equals(Namespaces.NS_XSD+"dateTime") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDateValue(arg, true);
-        } else if(node.getURI().equalsIgnoreCase("ABS") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg,typeCast == CastType.STRICT).abs();
-        } else if(node.getURI().equalsIgnoreCase("CEIL") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg,typeCast == CastType.STRICT).ceil();
-        } else if(node.getURI().equalsIgnoreCase("FLOOR") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg,typeCast == CastType.STRICT).floor();
-        } else if(node.getURI().equalsIgnoreCase("RAND") && node.getArgs().size() == 0) {
-            return create.rand();
-        } else if(node.getURI().equalsIgnoreCase("ROUND") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return getDoubleValue(arg,typeCast == CastType.STRICT).round();
-        } else if(node.getURI().equalsIgnoreCase("DAY") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.DAY);
-        } else if(node.getURI().equalsIgnoreCase("HOURS") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.HOUR);
-        } else if(node.getURI().equalsIgnoreCase("MINUTES") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.MINUTE);
-        } else if(node.getURI().equalsIgnoreCase("MONTH") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.MONTH);
-        } else if(node.getURI().equalsIgnoreCase("NOW") && node.getArgs().size() == 0) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.currentTimestamp();
-        } else if(node.getURI().equalsIgnoreCase("SECONDS") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.SECOND);
-        } else if(node.getURI().equalsIgnoreCase("YEAR") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.extract(getDateValue(arg,true),DatePart.YEAR);
-        } else if(node.getURI().equalsIgnoreCase("CONCAT") && node.getArgs().size() >= 1) {
-            ArrayList<Field> fields = new ArrayList<Field>(node.getArgs().size());
-            for(ValueExpr expr : node.getArgs()) {
-                Field result = getValue(meetValueExpression(node.getArgs().get(0)),true);
-                fields.add(result);
-            }
-
-            return create.concat(fields.toArray(new Field[0]));
-        } else if(node.getURI().equalsIgnoreCase("STRLEN") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.length(getValue(arg, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("SUBSTR") && node.getArgs().size() >= 2) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-            Field<Long> startPos = getIntegerValue(meetValueExpression(node.getArgs().get(1)),true);
-
-            if(node.getArgs().size() == 3) {
-                Field<Long> endPos = getIntegerValue(meetValueExpression(node.getArgs().get(2)),true);
-                return create.substring(getValue(arg,typeCast == CastType.STRICT),startPos,endPos);
-            } else {
-                return create.substring(getValue(arg, typeCast == CastType.STRICT), startPos);
-            }
-        } else if(node.getURI().equalsIgnoreCase("UCASE") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.upper(getValue(arg, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("LCASE") && node.getArgs().size() == 1) {
-            QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-            return create.lower(getValue(arg, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("STRSTARTS") && node.getArgs().size() == 2) {
-            QueryPart arg1 = meetValueExpression(node.getArgs().get(0));
-            QueryPart arg2 = meetValueExpression(node.getArgs().get(1));
-
-            return getValue(arg1,typeCast == CastType.STRICT).startsWith(getValue(arg2, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("STRENDS") && node.getArgs().size() == 2) {
-            QueryPart arg1 = meetValueExpression(node.getArgs().get(0));
-            QueryPart arg2 = meetValueExpression(node.getArgs().get(1));
-
-            return getValue(arg1,typeCast == CastType.STRICT).endsWith(getValue(arg2, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("STRENDS") && node.getArgs().size() == 2) {
-            QueryPart arg1 = meetValueExpression(node.getArgs().get(0));
-            QueryPart arg2 = meetValueExpression(node.getArgs().get(1));
-
-            return getValue(arg1,typeCast == CastType.STRICT).contains(getValue(arg2, typeCast == CastType.STRICT));
-        } else if(node.getURI().equalsIgnoreCase("STRBEFORE") && node.getArgs().size() == 2) {
-            QueryPart arg1 = meetValueExpression(node.getArgs().get(0));
-            QueryPart arg2 = meetValueExpression(node.getArgs().get(1));
-
-            return create.substring(getValue(arg1, typeCast == CastType.STRICT), create.val(0), create.position(getValue(arg1, typeCast == CastType.STRICT), getValue(arg2, typeCast == CastType.STRICT)));
-        } else if(node.getURI().equalsIgnoreCase("STRAFTER") && node.getArgs().size() == 2) {
-            QueryPart arg1 = meetValueExpression(node.getArgs().get(0));
-            QueryPart arg2 = meetValueExpression(node.getArgs().get(1));
-
-            Field val1 = getValue(arg1,typeCast == CastType.STRICT);
-            Field val2 = getValue(arg2,typeCast == CastType.STRICT);
-
-            return create.substring(val1,create.position(val1,val2).add(create.length(val2)),create.length(val1));
-        } else if(node.getURI().equalsIgnoreCase("MD5") && node.getArgs().size() == 1) {
-            if(dialect == SQLDialect.MYSQL || dialect == SQLDialect.POSTGRES) {
-                QueryPart arg = meetValueExpression(node.getArgs().get(0));
-
-                return create.field("MD5({0})",String.class,getValue(arg,typeCast == CastType.STRICT));
-            } else {
-                throw new UnsupportedOperationException("computing MD5 sum is only supported by PostgreSQL and MySQL backends");
-            }
-        }
-
-
-        throw new UnsupportedOperationException("function call "+node.getURI()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public List<JoinTable> group(Group node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-         for(String elem : node.getGroupBindingNames()) {
-            groupBy.add(elem);
-        }
-        return meetTableLike(node.getArg(), query, conditions, projections, tables);
-    }
-
-
-    public QueryPart groupConcat(GroupConcat node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-
-    public Field ifCond(If node)  {
-        QueryPart condition = meetValueExpression(node.getCondition());
-        QueryPart result    = meetValueExpression(node.getResult());
-        QueryPart alternative = meetValueExpression(node.getAlternative());
-
-        if(condition instanceof Condition) {
-            Field resultValue = null, alternativeValue = null;
-            if(result instanceof Table) {
-                resultValue = getValue((Table)result, true);
-            } else if(result instanceof Field) {
-                resultValue = (Field) result;
-            }
-            if(alternative instanceof Table) {
-                alternativeValue = getValue((Table)alternative, true);
-            } else if(alternative instanceof Field) {
-                alternativeValue = (Field)alternative;
-            }
-            if(resultValue != null && alternativeValue != null) {
-                return create.decode().when((Condition)condition, resultValue).otherwise(alternativeValue);
-            }
-        }
-
-        throw new IllegalArgumentException("incorrect argument types for IF .. THEN .. ELSE");
-    }
-
-
-    public QueryPart inCond(In node)  {
-        // TODO: how to deal with values vs. ids of a subselect?
-        /*
-        QueryPart subquery = meetTupleExpression(node.getSubQuery());
-        QueryPart value    = meetValueExpression(node.getArg());
-        */
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-
-    public List<JoinTable> intersection(Intersection node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections,Collection<Table> tables)  {
-        return merge(node,query,MergeType.INTERSECTION, conditions,  projections, tables);
-    }
-
-
-    public QueryPart iriFunction(IRIFunction node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public Condition isBNode(IsBNode node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof TNodes) {
-            Field<String> nodetype = ((TNodes)part).NODETYPE;
-
-            return nodetype.equal("ANON");
-        } else {
-            throw new IllegalArgumentException("argument of IsBNode must be a variable");
-        }
-    }
-
-
-    public Condition isLiteral(IsLiteral node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table) {
-            Field<String> nodetype = ((TNodes)part).NODETYPE;
-
-            return nodetype.equal("STRING").or(nodetype.equal("INTEGER")).or(nodetype.equal("DOUBLE"));
-        } else if(part instanceof Field) {
-            return create.trueCondition();
-        } else {
-            throw new IllegalArgumentException("argument of IsLiteral must be a variable or a constant");
-        }
-    }
-
-
-    public Condition isNumeric(IsNumeric node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table) {
-            Field<String> nodetype = ((TNodes)part).NODETYPE;
-
-            return nodetype.equal("INTEGER").or(nodetype.equal("DOUBLE"));
-        } else {
-            throw new IllegalArgumentException("argument of IsNumeric must be a variable");
-        }
-    }
-
-
-    public Condition isResource(IsResource node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table) {
-            Field<String> nodetype = ((TNodes)part).NODETYPE;
-
-            return nodetype.equal("URI").or(nodetype.equal("ANON"));
-        } else {
-            throw new IllegalArgumentException("argument of IsResource must be a variable");
-        }
-    }
-
-
-    public Condition isURI(IsURI node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table) {
-            Field<String> nodetype = ((TNodes)part).NODETYPE;
-
-            return nodetype.equal("URI");
-        } else {
-            throw new IllegalArgumentException("argument of IsURI must be a variable");
-        }
-    }
-
-
-    public List<JoinTable> join(Join node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-
-        List<JoinTable> resultTables = new ArrayList<JoinTable>();
-
-        resultTables.addAll(meetTableLike(node.getLeftArg(), query, conditions,  projections, tables));
-        resultTables.addAll(meetTableLike(node.getRightArg(), query, conditions, projections, tables));
-
-        return resultTables;
-    }
-
-
-    public Field label(Label node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table) {
-            return getValue((Table) part, true);
-        } else if(part instanceof Field) {
-            return (Field)part;
-        } else {
-            throw new IllegalArgumentException("argument of IsURI must be a variable");
-        }
-    }
-
-
-    public Field lang(Lang node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof TNodes) {
-            Field lang = ((TNodes)part).LANGUAGE;
-
-            return create.coalesce(lang, create.val(""));
-        } else if(part instanceof Field) {
-            return create.val("");
-        } else {
-            throw new IllegalArgumentException("argument of Lang must be a variable or constant");
-        }
-    }
-
-
-    public Condition langMatches(LangMatches node)  {
-        QueryPart leftPart = meetValueExpression(node.getLeftArg());
-        QueryPart rightPart = meetValueExpression(node.getRightArg());
-
-        if(dialect == SQLDialect.POSTGRES) {
-            // Postgres supports ILIKE
-            return create.condition(getValue(leftPart, true)+" ILIKE "+create.decode().value(getValue(rightPart, true)).when("*", create.val("%")).otherwise(getValue(rightPart, true).concat("%")));
-        } else {
-            return getValue(leftPart, true).lower().like(create.decode().value(getValue(rightPart, true)).when("*", create.val("%")).otherwise(getValue(rightPart, true).lower().concat("%")));
-        }
-    }
-
-
-    public List<JoinTable> leftJoin(LeftJoin node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections,Collection<Table> tables)  {
-        Set<Condition> conditions2 = new HashSet<Condition>();
-        // this belongs to the join condition!
-        if(node.getCondition() != null) {
-            QueryPart conditionPart = meetValueExpression(node.getCondition());
-            conditions2.add((Condition)conditionPart);
-        }
-
-        List<JoinTable> leftTables = meetTableLike(node.getLeftArg(), query, conditions,  projections, tables);
-
-        Table left = null;
-        for(JoinTable joinTable : leftTables) {
-            if(left == null) {
-                left = joinTable.getTable();
-                conditions.addAll(joinTable.getConditions());
-            } else {
-                left = left.join(joinTable.getTable()).on(joinTable.getConditions().toArray(new Condition[0]));
-            }
-        }
-
-        List<JoinTable> rightTables = meetTableLike(node.getRightArg(), query, conditions2,  projections, tables);
-        Table right = null;
-        for(JoinTable joinTable : rightTables) {
-            if(right == null) {
-                right = joinTable.getTable();
-                conditions2.addAll(joinTable.getConditions());
-            } else {
-                Set<Condition> onConditions = new HashSet<Condition>();
-                Set<Condition> backConditions = joinTable.getBackConditions();
-                for(Condition c : joinTable.getConditions()) {
-                    if(!backConditions.contains(c)) {
-                        onConditions.add(c);
-                    }
-                }
-
-                right = right.join(joinTable.getTable()).on(onConditions.toArray(new Condition[0]));
-                conditions2.addAll(backConditions);
-            }
-        }
-
-        if(left != null && right != null) {
-            return Collections.singletonList(new JoinTable((Table)left.leftOuterJoin(right).on(conditions2.toArray(new Condition[0]))));
-        } else {
-            conditions.addAll(conditions2);
-            return Collections.singletonList(new JoinTable((Table) left != null? left : right));
-        }
-
-
-    }
-
-
-    public Condition like(Like node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        Condition result = null;
-        for(Field f : getAlternativeValues(part, true)) {
-            if(result == null) {
-                result = f.like(node.getOpPattern());
-            } else {
-                result = result.or(f.like(node.getOpPattern()));
-            }
-        }
-
-        return result;
-    }
-
-
-
-
-    /**
-     * Mathematical expression on the values of the two arguments of the expression. We implement this by
-     * always retrieving the double value of the two arguments and then performing the corresponding mathematical
-     * operation on the SQL level.
-     * @param node
-     * @return
-     */
-    public Field mathExpr(MathExpr node)  {
-        QueryPart leftPart = meetValueExpression(node.getLeftArg());
-        QueryPart rightPart = meetValueExpression(node.getRightArg());
-
-        Field left, right;
-
-        left = getDoubleValue(leftPart,typeCast == CastType.STRICT);
-        right = getDoubleValue(rightPart,typeCast == CastType.STRICT);
-
-        switch (node.getOperator()) {
-            case DIVIDE:
-                return left.div(right);
-            case MINUS:
-                return left.sub(right);
-            case MULTIPLY:
-                return left.mul(right);
-            case PLUS:
-                return left.add(right);
-            default:
-                throw new IllegalArgumentException("unknown operator: "+node.getOperator());
-        }
-
-
-    }
-
-
-    /**
-     * Return the maximum value of the arguments. Translated to SQL max() function
-     * @param node
-     * @return
-     */
-    public Field max(Max node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table && ((Table) part).getName().equals(T_NODES.getName())) {
-            return getValue((Table)part, true).max();
-        } else {
-            throw new IllegalArgumentException("MAX can only be computed for the node table; type was: "+part.getClass().getName());
-        }
-    }
-
-
-    /**
-     * Return the minimum value of the arguments. Translated to SQL min() function
-     * @param node
-     * @return
-     */
-    public Field min(Min node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        if(part instanceof Table && ((Table) part).getName().equals(T_NODES.getName())) {
-            return getValue((Table)part, true).min();
-        } else {
-            throw new IllegalArgumentException("MAX can only be computed for the node table; type was: "+part.getClass().getName());
-        }
-    }
-
-
-
-
-    public Select multiProjection(MultiProjection node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-    /**
-     * Namespace querying. Currently not supported by the translator. Could be implemented either by using
-     * SQL string operations on the URI of the argument, or by joining with the namespace table and trying to
-     * find a prefix.
-     * @param node
-     * @return
-     */
-    public QueryPart namespace(Namespace node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-    /**
-     * Namespace querying. Currently not supported by the translator. Could be implemented either by using
-     * SQL string operations on the URI of the argument, or by joining with the namespace table and trying to
-     * find a prefix.
-     * @param node
-     * @return
-     */
-    public QueryPart localName(LocalName node)  {
-        // todo: would require querying against the namespace table as well!
-
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    /**
-     * NOT of a value expression. Translated into a NOT in case the argument is a condition, or
-     * a NEG in case the argument is a value.
-     * @param node
-     * @return
-     */
-    public QueryPart not(Not node)  {
-        QueryPart subPart = meetValueExpression(node.getArg());
-
-        if(subPart instanceof Condition) {
-            return ((Condition)subPart).not();
-        } else if(subPart instanceof Field) {
-            return ((Field)subPart).neg();
-        }
-
-        throw new IllegalStateException("the argument of the NOT condition is not boolean: "+node);
-    }
-
-    /**
-     * OR between value expressions; translated into a disjunction at the SQL level.
-     * @param node
-     * @return
-     */
-    public Condition or(Or node)  {
-        QueryPart leftPart = meetValueExpression(node.getLeftArg());
-        QueryPart rightPart = meetValueExpression(node.getRightArg());
-
-        if(! (leftPart instanceof Condition) || !(rightPart instanceof Condition)) {
-            throw new IllegalStateException("the left or right part of the OR condition are not boolean: "+node);
-        }
-
-        return ((Condition)leftPart).or((Condition) rightPart);
-    }
-
-    /**
-     * Ordering of query results. For each ordering used in the query, we keep track of a value expression
-     * that needs to be projected by all subqueries so we can later sort over the results of several subqueries
-     * (otherwise the SQL database might complain about ordering over non-projected variables, which is semantically
-     * not allowed in SQL).
-     *
-     * @param node
-     * @param query
-     * @param conditions
-     * @param projections
-     * @return
-     */
-    public Select order(Order node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        int i=0;
-        for(OrderElem elem : node.getElements()) {
-            QueryPart expr = meetValueExpression(elem.getExpr());
-            String name = "_order_" + (++i);
-            sortFields.put(name, getValue(expr, true).as(name));
-            sortDependencies.put(name,getValueExpressionVariables(elem.getExpr()));
-        }
-
-
-        Select select = meetTupleExpression(node.getArg(),query,conditions,  projections);
-        if(select instanceof SelectQuery) {
-            i=0;
-            for(OrderElem elem : node.getElements()) {
-                String name = "_order_" + (++i);
-                if(elem.isAscending()) {
-                    ((SelectQuery)select).addOrderBy(sortFields.get(name).asc());
-                } else {
-                    ((SelectQuery)select).addOrderBy(sortFields.get(name).desc());
-                }
-            }
-            return select;
-        } else {
-            List<SortField<?>> fields = new ArrayList<SortField<?>>();
-            i=0;
-            for(OrderElem elem : node.getElements()) {
-                String name = "_order_" + Math.abs(query.hashCode()) + "_" + (++i);
-                if(elem.isAscending()) {
-                    fields.add(sortFields.get(name).asc());
-                } else {
-                    fields.add(sortFields.get(name).desc());
-                }
-            }
-            return create.select().from(select).orderBy(fields);
-        }
-    }
-
-    /**
-     * Projection: for all variables (table KiWiNode) in the projection we select all fields and add them to the select
-     * part of the SQL query; this allows us to reconstruct KiWiNode instances in the query results
-     * @param node
-     * @param query
-     * @return
-     */
-    public Select projection(Projection node, SelectQuery query, Collection<Condition> origConditions, Collection<String> projections)  {
-        Set<String> projections2 = new HashSet<String>();
-
-        // collect mappings before running recursively so they are available to child expressions
-        for(ProjectionElem elem : node.getProjectionElemList().getElements()) {
-            variableMappings.put(elem.getSourceName().replace("-","_"),elem.getTargetName());
-            revVariableMappings.put(elem.getTargetName(),elem.getSourceName().replace("-","_"));
-            projections2.add(elem.getSourceName());
-        }
-
-
-        Set<Condition> conditions = new HashSet<Condition>();
-
-/*
-        Table from = null;
-        for(JoinTable tbl : meetTableLike(node.getArg(), query, conditions,  projections2, new HashSet<Table>())) {
-            if(from == null) {
-                from = tbl.getTable();
-                query.addConditions(tbl.getConditions());
-            } else {
-                from = from.join(tbl.getTable()).on(tbl.getConditions().toArray(new Condition[0]));
-            }
-        }
-        if(from != null)
-            query.addFrom(from);
-*/
-
-        for(JoinTable tbl : meetTableLike(node.getArg(), query, conditions,  projections2, new HashSet<Table>())) {
-                query.addFrom(tbl.getTable());
-                query.addConditions(tbl.getConditions());
-        }
-
-
-        query.addConditions(conditions);
-
-        if(groupBy.size() > 0) {
-            for(String group : groupBy) {
-                Field variable = extensions.get(group.replace("-","_"));
-                if(variable == null) {
-                    TNodes table = getVariable(group);
-                    if(table != null) {
-                        query.addGroupBy(table.ID);
-                        query.addGroupBy(table.URI);
-                        query.addGroupBy(table.ANONID);
-                        query.addGroupBy(table.CONTENT);
-                    }
-
-                } else {
-                    query.addGroupBy(variable);
-                }
-            }
-        }
-
-        if(node.getArg() instanceof Union || node.getArg() instanceof Intersection || node.getArg() instanceof Difference) {
-            // union, difference, intersection: we take all results, as the merge operation already does the projection
-            projectedVariables.addAll(node.getBindingNames());
-        } else {
-            for(ProjectionElem elem : node.getProjectionElemList().getElements()) {
-                projectionElem(elem, query);
-            }
-            for(Map.Entry<String,Field> entry : sortFields.entrySet()) {
-                if(!hasSelectionVariable(query,entry.getKey())) {
-                    Set<String> dependencies = sortDependencies.get(entry.getKey());
-                    boolean containsAll = true;
-                    for(String dep : dependencies) {
-                        if(!currentVariables.containsKey(dep) && !extensions.containsKey(dep)) {
-                            containsAll = false;
-                        }
-                    }
-                    if(containsAll) {
-                        query.addSelect(entry.getValue());
-                    } else {
-                        query.addSelect(create.value(null).as(entry.getKey()));
-                    }
-                }
-            }
-        }
-
-        return query;
-    }
-
-
-    public void projectionElem(ProjectionElem node, SelectQuery query)  {
-        // renaming needs to take place in the result construction!
-        TNodes var = getVariable(node.getSourceName());
-
-        // if var is null, then we have an extension
-        if(var != null) {
-            query.addSelect(var.ID.as(node.getTargetName())); // just the ID for now, we will use Hibernate to load the complete node
-            projectedVariables.add(node.getTargetName());
-        } else {
-            Field extension = extensions.get(node.getSourceName().replace("-","_"));
-            query.addSelect(extension.as(node.getTargetName()));
-            extensionVariables.put(node.getTargetName(), extension.getType());
-        }
-
-        // extension bindings need to be treated differently in result construction!
-    }
-
-
-
-
-    public Select queryRoot(QueryRoot node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        this.resourceVariables = new FindResourceVariables(node).getResourceVariables();
-
-        return meetTupleExpression(node.getArg(),query, conditions,  projections);
-    }
-
-
-    /**
-     * Reduced is a strange construct that means "sometimes distinct". We translate it into distinct in all cases.
-     * @param node
-     * @param query
-     * @param conditions
-     * @param projections
-     * @return
-     */
-    public Select reduced(Reduced node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-
-        if(configurationService.getBooleanConfiguration("sparql.native.reduced_as_distinct",false)) {
-
-            Select subQuery = meetTupleExpression(node.getArg(), query, conditions,  projections);
-
-            if(subQuery instanceof SelectQuery) {
-                ((SelectQuery) subQuery).setDistinct(true);
-                return subQuery;
-            } else {
-                return create.selectDistinct().from(subQuery);
-            }
-        } else {
-            return meetTupleExpression(node.getArg(), query, conditions,  projections);
-        }
-    }
-
-    /**
-     * Translate a regular expression into a corresponding database operator. Regular expressions are only supported
-     * in some databases (currently: Postgres, H2, Oracle, MySQL) and are in some implementations comparably slow, so
-     * use them with care.
-     * <p/>
-     * This method tries to translate simple regular expressions into LIKE operators, which are considerably more
-     * efficient to evaluate in many database systems. Currently, this is done for regular expressions that do not
-     * contain any special constructs, i.e. consist of alphanumeric characters and blanks only.
-     * @param node
-     * @return
-     */
-    public Condition regex(Regex node)  {
-        QueryPart argPart = meetValueExpression(node.getArg());
-
-        if(node.getPatternArg() instanceof ValueConstant) {
-            ValueConstant pat = (ValueConstant)node.getPatternArg();
-            String pattern = pat.getValue().stringValue();
-
-            Condition result = null;
-            Field f = getValue(argPart,typeCast == CastType.STRICT);
-
-            // simple cases can be handled by LIKE
-            if(pattern.matches("^\\^?[\\p{Alnum}\\p{Blank}]+$")) {
-                if(pattern.startsWith("^")) {
-                    result = f.like(pattern.substring(1) + "%");
-                } else {
-                    result = f.like("%" + pattern + "%");
-                }
-            } else {
-                switch (dialect) {
-                    case POSTGRES:
-                        result = create.condition(f + " ~ ?",pattern);
-                        break;
-                    case H2:
-                        result = create.condition(f + " REGEXP ?",pattern);
-                        break;
-                    case MYSQL:
-                        result = create.condition(f + " REGEXP ?",pattern);
-                        break;
-                    case ORACLE:
-                        result = create.condition("REGEXP_LIKE("+f + ",?)" ,pattern);
-                        break;
-                }
-            }
-            return result;
-        } else {
-            QueryPart patPart = meetValueExpression(node.getPatternArg());
-            switch (dialect) {
-                case POSTGRES:
-                    return create.condition(getValue(argPart, typeCast == CastType.STRICT) + " ~ " + getValue(patPart, typeCast == CastType.STRICT));
-                case H2:
-                    return create.condition(getValue(argPart, typeCast == CastType.STRICT) + " REGEXP " + getValue(patPart, typeCast == CastType.STRICT));
-                case MYSQL:
-                    return create.condition(getValue(argPart, typeCast == CastType.STRICT) + " REGEXP " + getValue(patPart, typeCast == CastType.STRICT));
-                case ORACLE:
-                    return create.condition("REGEXP_LIKE("+getValue(argPart, typeCast == CastType.STRICT) + "," + getValue(patPart, typeCast == CastType.STRICT)+")");
-
-            }
-        }
-        throw new UnsupportedOperationException("database "+dialect+" not supported for regular expression matches");
-    }
-
-    /**
-     * Check whether the left and the right argument are the same term. In case both arguments identify variables,
-     * we translate this into a check for equality of database identifiers, as this is most efficient. In all other
-     * cases we check equality of the content
-     * @param node
-     * @return
-     */
-    public QueryPart sameTerm(SameTerm node)  {
-        QueryPart leftPart = meetValueExpression(node.getLeftArg());
-        QueryPart rightPart = meetValueExpression(node.getRightArg());
-
-        if(leftPart instanceof TNodes && rightPart instanceof TNodes) {
-            return ((TNodes) leftPart).ID.equal(((TNodes) rightPart).ID);
-        } else if(leftPart instanceof TNodes && rightPart instanceof Field) {
-            // check if one of the value-holding fields of leftpart matches rightpart
-            Condition result = null;
-            for(Field f : getAlternativeValues(leftPart,false)) {
-                if(result == null) {
-                    result = f.equal((Field)rightPart);
-                } else {
-                    result = result.or(f.equal((Field)rightPart));
-                }
-            }
-            return result;
-        } else if(rightPart instanceof TNodes && leftPart instanceof Field) {
-            // check if one of the value-holding fields of leftpart matches rightpart
-            Condition result = null;
-            for(Field f : getAlternativeValues(rightPart,false)) {
-                if(result == null) {
-                    result = f.equal((Field)leftPart);
-                } else {
-                    result = result.or(f.equal((Field)leftPart));
-                }
-            }
-            return result;
-        } else {
-            // TODO: language tags for literals?
-            return getValue(leftPart, true).equal(getValue(rightPart, true));
-        }
-    }
-
-
-    public QueryPart sample(Sample node)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public Select service(Service node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        throw new UnsupportedOperationException(node.getClass().getName()+" not supported");    //To change body of overridden methods use File | Settings | File Templates.
-    }
-
-
-    public Select singletonSet(SingletonSet node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        query.addConditions(create.trueCondition());
-        return query;
-    }
-
-
-    public Select slice(Slice node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections)  {
-        query.addLimit(node.hasOffset() ? (int) node.getOffset() : 0, node.hasLimit() ? (int) node.getLimit() : 0);
-        if(node.getArg() instanceof Projection || node.getArg() instanceof Distinct || node.getArg() instanceof Reduced || node.getArg() instanceof Order) {
-            return meetTupleExpression(node.getArg(), query, conditions,  projections);
-        } else {
-            List<Table> tables = new ArrayList<Table>();
-            Table from = null;
-            for(JoinTable tbl : meetTableLike(node.getArg(), query, conditions,  node.getBindingNames(),tables)) {
-                if(from == null) {
-                    from = tbl.getTable();
-                    query.addConditions(tbl.getConditions());
-                } else {
-                    from = from.join(tbl.getTable()).on(tbl.getConditions().toArray(new Condition[0]));
-                }
-            }
-            query.addFrom(from);
-            query.addConditions(conditions);
-            if(tables.size() > 0 && tables.get(0) instanceof TTriples) {
-                query.addSelect(((TTriples) tables.get(0)).ID.as("_firsttable"));
-            }
-            return query;
-        }
-    }
-
-
-    public List<JoinTable> statementPattern(StatementPattern p, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-        String name = "t"+ Math.abs(++tripleCounter);
-
-        // statement pattern; we add a triple to the from clause and require it is not deleted; then we add
-        // conditions for subject, predicate, object, context depending on whether they are variable or
-        // constant values
-
-        TTriples triple = T_TRIPLES.as(name);
-        JoinTable j_triple = new JoinTable(triple);
-        j_triple.addCondition(triple.DELETED.isFalse());
-        tables.add(triple);
-
-        TNodes t_subject = null, t_property = null, t_object = null, t_context = null;
-        JoinTable j_subject = null, j_property = null, j_object = null, j_context = null;
-
-        List<JoinTable> resultTables = new ArrayList<JoinTable>();
-
-
-        resultTables.add(j_triple);
-
-
-        // conditions for subject:
-        // - if there is a value, and the value is a KiWiNode, simply check the ID (most efficient query)
-        // - if there is a value, but it is not a KiWiNode, check the properties depending on the type of value
-        // - if there is no value, add a variable to the from clause and add a join condition
-        Var subj = p.getSubjectVar();
-        if(subj.hasValue()) {
-            Value v = subj.getValue();
-            t_subject =  T_NODES.as(name+"_subject");
-            j_subject = new JoinTable(t_subject);
-
-            if(v instanceof KiWiNode && ((KiWiNode) v).getId() != null) {
-                KiWiNode n = (KiWiNode) v;
-                j_triple.addCondition(triple.SUBJECT_ID.equal((Field) create.val(n.getId())));
-            } else if(v instanceof URI) {
-
-                if(configurationService.getBooleanConfiguration("sparql.native.preload_constants",true)) {
-                    KiWiUriResource r_subject = resourceService.getUriResource(v.stringValue());
-                    if(r_subject != null) {
-                        j_triple.addCondition(triple.SUBJECT_ID.equal((Field) create.val(r_subject.getId())));
-                    } else {
-                        j_triple.addCondition(create.falseCondition());
-                    }
-                } else {
-                    // performance improvement: if uri already was used, reuse the node instead of doing a new join
-                    if(uriNodes.containsKey(v.stringValue())) {
-                        t_subject = uriNodes.get(v.stringValue());
-                        Condition c_subject = triple.SUBJECT_ID.equal((Field) t_subject.ID);
-                        j_triple.addCondition(c_subject);
-                        j_triple.addBackCondition(c_subject);
-                    } else {
-                        resultTables.add(j_subject);
-                        j_subject.addCondition(t_subject.URI.equal((Field) create.val(v.stringValue())));
-                        j_subject.addCondition(triple.SUBJECT_ID.equal((Field) t_subject.ID));
-                        uriNodes.put(v.stringValue(),t_subject);
-                    }
-                }
-
-            } else if(v instanceof BNode) {
-                resultTables.add(j_subject);
-                j_subject.addCondition(t_subject.ANONID.equal((Field) create.val(((BNode) v).getID())));
-                j_subject.addCondition(triple.SUBJECT_ID.equal((Field) t_subject.ID));
-            } else {
-                throw new UnsupportedOperationException("value of type "+v.getClass()+" not supported!");
-            }
-        } else {
-            String varname = subj.getName().replace("-", "_");
-
-            t_subject = getVariable(varname);
-            if(!hasQueryVariable(query,varname)) {
-                // variable does not exist yet, so we create it and join it to the current from clause ...
-                t_subject = createVariable(varname);
-                addQueryVariable(query,varname,t_subject);
-                j_subject = new JoinTable(t_subject);
-                j_subject.addCondition(triple.SUBJECT_ID.equal((Field) t_subject.ID));
-                resultTables.add(j_subject);
-            } else {
-                // variable already exists in FROM, we simply add a join condition
-                Condition c_subject = triple.SUBJECT_ID.equal((Field) t_subject.ID);
-                j_triple.addCondition(c_subject);
-                j_triple.addBackCondition(c_subject);
-            }
-        }
-
-        Var prop = p.getPredicateVar();
-        if(prop.hasValue()) {
-            Value v = prop.getValue();
-            t_property = T_NODES.as(name+"_property");
-            j_property = new JoinTable(t_property);
-
-            if(v instanceof KiWiNode && ((KiWiNode) v).getId() != null) {
-                KiWiNode n = (KiWiNode) v;
-                j_triple.addCondition(triple.PROPERTY_ID.equal((Field) create.val(n.getId())));
-            } else if(v instanceof URI) {
-                if(configurationService.getBooleanConfiguration("sparql.native.preload_constants",true)) {
-                    KiWiUriResource r_property = resourceService.getUriResource(v.stringValue());
-                    if(r_property != null) {
-                        j_triple.addCondition(triple.PROPERTY_ID.equal((Field) create.val(r_property.getId())));
-                    } else {
-                        j_triple.addCondition(create.falseCondition());
-                    }
-                } else {
-                    // performance improvement: if uri already was used, reuse the node instead of doing a new join
-                    if(uriNodes.containsKey(v.stringValue())) {
-                        t_property = uriNodes.get(v.stringValue());
-                        Condition c_property = triple.PROPERTY_ID.equal((Field) t_property.ID);
-                        j_triple.addCondition(c_property);
-                        j_triple.addBackCondition(c_property);
-                    } else {
-                        resultTables.add(j_property);
-                        j_property.addCondition(t_property.URI.equal((Field) create.val(v.stringValue())));
-                        j_property.addCondition(triple.PROPERTY_ID.equal((Field) t_property.ID));
-                        uriNodes.put(v.stringValue(),t_property);
-                    }
-                }
-
-
-            } else {
-                throw new UnsupportedOperationException("value of type "+v.getClass()+" not supported!");
-            }
-        } else {
-            String varname = prop.getName().replace("-","_");
-
-            t_property = getVariable(varname);
-            if(!hasQueryVariable(query,varname)) {
-                // variable does not exist yet, so we create it and join it to the current from clause ...
-                t_property = createVariable(varname);
-                addQueryVariable(query,varname,t_property);
-                j_property = new JoinTable(t_property);
-                j_property.addCondition(triple.PROPERTY_ID.equal((Field) t_property.ID));
-                resultTables.add(j_property);
-            } else {
-                // variable already exists in FROM, we simply add a join condition
-                Condition c_property = triple.PROPERTY_ID.equal((Field) t_property.ID);
-                j_triple.addCondition(c_property);
-                j_triple.addBackCondition(c_property);
-            }
-        }
-
-        Var obj  = p.getObjectVar();
-        if(obj.hasValue()) {
-            Value v = obj.getValue();
-            t_object = T_NODES.as(name+"_object");
-            j_object = new JoinTable(t_object);
-
-            if(v instanceof KiWiNode && ((KiWiNode) v).getId() != null) {
-                KiWiNode n = (KiWiNode) v;
-                j_triple.addCondition(triple.OBJECT_ID.equal((Field) create.val(n.getId())));
-            } else if(v instanceof URI) {
-                if(configurationService.getBooleanConfiguration("sparql.native.preload_constants",true)) {
-                    KiWiUriResource r_object = resourceService.getUriResource(v.stringValue());
-                    if(r_object != null) {
-                        j_triple.addCondition(triple.OBJECT_ID.equal((Field) create.val(r_object.getId())));
-                    } else {
-                        j_triple.addCondition(create.falseCondition());
-                    }
-                } else {
-                    // performance improvement: if uri already was used, reuse the node instead of doing a new join
-                    if(uriNodes.containsKey(v.stringValue())) {
-                        t_object = uriNodes.get(v.stringValue());
-                        Condition c_object = triple.OBJECT_ID.equal((Field) t_object.ID);
-                        j_triple.addCondition(c_object);
-                        j_triple.addBackCondition(c_object);
-                    } else {
-                        resultTables.add(j_object);
-                        j_object.addCondition(t_object.URI.equal((Field) create.val(v.stringValue())));
-                        j_object.addCondition(triple.OBJECT_ID.equal((Field) t_object.ID));
-                        uriNodes.put(v.stringValue(),t_object);
-                    }
-                }
-
-            } else if(v instanceof BNode) {
-                resultTables.add(j_object);
-                j_object.addCondition(t_object.ANONID.equal((Field) create.val(((BNode) v).getID())));
-                j_object.addCondition(triple.OBJECT_ID.equal((Field) t_object.ID));
-            } else if(v instanceof Literal) {
-                resultTables.add(j_object);
-                j_object.addCondition(t_object.CONTENTMD5.equal((Field) create.val(HashUtils.md5sum(v.stringValue()))));
-                j_object.addCondition(triple.OBJECT_ID.equal((Field) t_object.ID));
-            } else {
-                throw new UnsupportedOperationException("value of type "+v.getClass()+" not supported!");
-            }
-        } else  {
-            String varname = obj.getName().replace("-","_");
-
-            t_object = getVariable(varname);
-            if(!hasQueryVariable(query,varname)) {
-                // variable does not exist yet, so we create it and join it to the current from clause ...
-                t_object = createVariable(varname);
-                addQueryVariable(query,varname,t_object);
-                j_object = new JoinTable(t_object);
-                j_object.addCondition(triple.OBJECT_ID.equal((Field) t_object.ID));
-                resultTables.add(j_object);
-            } else {
-                // variable already exists in FROM, we simply add a join condition
-                Condition c_object = triple.OBJECT_ID.equal((Field) t_object.ID);
-                j_triple.addCondition(c_object);
-                j_triple.addBackCondition(c_object);
-            }
-        }
-
-        Var ctx  = p.getContextVar();
-        if(ctx != null) {
-            if(ctx.hasValue()) {
-                Value v = ctx.getValue();
-                t_context =  T_NODES.as(name+"_context");
-                j_context = new JoinTable(t_context);
-
-                if(v instanceof KiWiNode && ((KiWiNode) v).getId() != null) {
-                    KiWiNode n = (KiWiNode) v;
-                    j_triple.addCondition(triple.CONTEXT_ID.equal((Field) create.val(n.getId())));
-                } else if(v instanceof URI) {
-                    if(configurationService.getBooleanConfiguration("sparql.native.preload_constants",true)) {
-                        KiWiUriResource r_context = resourceService.getUriResource(v.stringValue());
-                        if(r_context != null) {
-                            j_triple.addCondition(triple.CONTEXT_ID.equal((Field) create.val(r_context.getId())));
-                        } else {
-                            j_triple.addCondition(create.falseCondition());
-                        }
-                    } else {
-                        // performance improvement: if uri already was used, reuse the node instead of doing a new join
-                        if(uriNodes.containsKey(v.stringValue())) {
-                            t_context = uriNodes.get(v.stringValue());
-                            Condition c_context = triple.CONTEXT_ID.equal((Field) t_context.ID);
-                            j_triple.addCondition(c_context);
-                            j_triple.addBackCondition(c_context);
-                        } else {
-                            resultTables.add(j_context);
-                            j_context.addCondition(t_context.URI.equal((Field) create.val(v.stringValue())));
-                            j_context.addCondition(triple.CONTEXT_ID.equal((Field) t_context.ID));
-                            uriNodes.put(v.stringValue(),t_context);
-                        }
-                    }
-
-                } else if(v instanceof BNode) {
-                    resultTables.add(j_context);
-                    j_context.addCondition(t_context.ANONID.equal((Field) create.val(((BNode) v).getID())));
-                    j_context.addCondition(triple.CONTEXT_ID.equal((Field) t_context.ID));
-                } else {
-                    throw new UnsupportedOperationException("value of type "+v.getClass()+" not supported!");
-                }
-            } else {
-                String varname = ctx.getName().replace("-","_");
-
-                t_context = getVariable(varname);
-                if(!hasQueryVariable(query,varname)) {
-                    // variable does not exist yet, so we create it and join it to the current from clause ...
-                    t_context = createVariable(varname);
-                    addQueryVariable(query,varname,t_context);
-                    j_context = new JoinTable(t_context);
-                    j_context.addCondition(triple.CONTEXT_ID.equal((Field) t_context.ID));
-                    resultTables.add(j_context);
-                } else {
-                    // variable already exists in FROM, we simply add a join condition
-                    Condition c_context = triple.CONTEXT_ID.equal((Field) t_context.ID);
-                    j_triple.addCondition(c_context);
-                    j_triple.addBackCondition(c_context);
-                }
-            }
-        }
-
-        return resultTables;
-
-    }
-
-
-    public Field str(Str node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        return getValue(part, true);
-    }
-
-
-    public Field sum(Sum node)  {
-        QueryPart part = meetValueExpression(node.getArg());
-
-        return getDoubleValue(part, typeCast == CastType.STRICT).sum();
-    }
-
-
-    private List<JoinTable> unionTable(Union node, SelectQuery query, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables)  {
-        return merge(node, query, MergeType.UNION, conditions, projections, tables);
-    }
-
-
-    // special case: union occurring as tuple expression, not as table; this is typically the result of a multi-projection
-    private Select unionQuery(Union node, SelectQuery query,Collection<Condition> conditions, Collection<String> projections) {
-        // the bindings in proper order
-        List<String> bindings = new ArrayList<String>();
-        for(String b : node.getBindingNames()) {
-            if(!b.startsWith("-const") && projections.contains(b)) {
-                bindings.add(b);
-            }
-        }
-
-        Map<String,TNodes> contextVars = currentVariables;
-        Map<String,TNodes> contextUris = uriNodes;
-
-        // build subquery for left part of the binary tuple query
-        currentVariables = new HashMap<String, TNodes>();
-        uriNodes         = new HashMap<String, TNodes>();
-        Set<Condition> leftConditions = new HashSet<Condition>();
-        SelectQuery leftQuery = create.selectQuery();
-        leftQuery.addFrom(meetTupleExpression(node.getLeftArg(), create.selectQuery(), leftConditions,  projections));
-        if(leftConditions.size() > 0) {
-            leftQuery.addConditions(leftConditions);
-        }
-
-        // for each of the projected variables of the main query, add a projection to the subquery; if the projection
-        // variable is not bound in this subquery, bind it explicitly to NULL
-        for(String var : bindings) {
-            var = var.replace("-","_");
-            String revVar = revVariableMappings.get(var);
-
-            if(!hasSelectionVariable(leftQuery,var)) {
-
-                if(currentVariables.containsKey(var)) {
-                    leftQuery.addSelect(currentVariables.get(var).ID.as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else if(extensions.containsKey(var)) {
-                    leftQuery.addSelect(extensions.get(var).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else if(revVar != null && extensions.containsKey(revVar)) {
-                    leftQuery.addSelect(extensions.get(revVar).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else {
-                    leftQuery.addSelect(create.value(null,Long.class).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                }
-            }
-        }
-        // for each of the fields used in sorting the overall result, add an additional column to the projection so
-        // that we can afterwards sort easily over the UNION
-        for(Map.Entry<String,Field> entry : sortFields.entrySet()) {
-            if(!hasSelectionVariable(leftQuery,entry.getKey())) {
-                Set<String> dependencies = sortDependencies.get(entry.getKey());
-                boolean containsAll = true;
-                for(String dep : dependencies) {
-                    if(!currentVariables.containsKey(dep) && !extensions.containsKey(dep)) {
-                        containsAll = false;
-                    }
-                }
-                if(containsAll) {
-                    leftQuery.addSelect(entry.getValue());
-                } else {
-                    leftQuery.addSelect(create.value(null).as(entry.getKey()));
-                }
-            }
-        }
-
-        currentVariables = new HashMap<String, TNodes>();
-        uriNodes         = new HashMap<String, TNodes>();
-        Set<Condition> rightConditions = new HashSet<Condition>();
-        SelectQuery rightQuery = create.selectQuery();
-        rightQuery.addFrom(meetTupleExpression(node.getRightArg(), create.selectQuery(), rightConditions,  projections));
-        rightQuery.addConditions(rightConditions);
-
-        for(String var : bindings) {
-            var = var.replace("-","_");
-            String revVar = revVariableMappings.get(var);
-
-            if(!hasSelectionVariable(rightQuery,var)) {
-
-                if(currentVariables.containsKey(var)) {
-                    rightQuery.addSelect(currentVariables.get(var).ID.as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else if(extensions.containsKey(var)) {
-                    rightQuery.addSelect(extensions.get(var).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else if(revVar != null && extensions.containsKey(revVar)) {
-                    rightQuery.addSelect(extensions.get(revVar).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                } else {
-                    rightQuery.addSelect(create.value(null,Long.class).as(variableMappings.containsKey(var)?variableMappings.get(var):var));
-                }
-            }
-        }
-        for(Map.Entry<String,Field> entry : sortFields.entrySet()) {
-            if(!hasSelectionVariable(rightQuery,entry.getKey())) {
-                Set<String> dependencies = sortDependencies.get(entry.getKey());
-                boolean containsAll = true;
-                for(String dep : dependencies) {
-                    if(!currentVariables.containsKey(dep) && !extensions.containsKey(dep)) {
-                        containsAll = false;
-                    }
-                }
-                if(containsAll) {
-                    rightQuery.addSelect(entry.getValue());
-                } else {
-                    rightQuery.addSelect(create.value(null).as(entry.getKey()));
-                }
-            }
-        }
-
-        currentVariables = contextVars;
-        uriNodes         = contextUris;
-
-        return leftQuery.union(rightQuery);
-     }
-
-    /**
-     * Merge the results of two subqueries using either UNION, DIFFERENCE, or INTERSECTION.
-     * Note that UNION & co in SPARQL and SQL have slightly different semantics: whereas SQL requires an equal number
-     * of columns (of equal types) in the subqueries to carry out the UNION, SPARQL performs the UNION on the names of
-     * the variables; it does not require that all variables are bound in all query parts.
-     * <p/>
-     * In order to model this behaviour in SQL, this method performs the following steps:
-     * <ul>
-     *     <li>build separate subqueries for each of the parts of the union</li>
-     *     <li>find out which variables to project in which order, and which variables need to be bound to NULL
-     *         in one of the subqueries because they are not otherwise bound</li>
-     *     <li>find out which of the variables that are NOT projected might be required for sorting the overall
-     *         result, and add these to the projections of the subqueries</li>
-     * </ul>
-     * @param node
-     * @param query
-     * @param op
-     * @param conditions
-     * @param projections
-     * @param tables
-     * @return
-     */
-    public List<JoinTable> merge(BinaryTupleOperator node, SelectQuery query, MergeType op, Collection<Condition> conditions, Collection<String> projections, Collection<Table> tables )  {
-        // the bindings in proper order
-        List<String> bindings = new ArrayList<String>();
-        for(String b : node.getBindingNames()) {
-            if(!b.startsWith("-const") && projections.contains(b)) {
-                bindings.add(b);
-            }
-        }
-
-        Map<String,TNodes> contextVars = currentVariables;
-        Map<String,TNodes> contextUris = uriNodes;
-
-        // build subquery for left part of the binary tuple query
-        currentVariables = new HashMap<String, TNodes>();
-        uriNodes         = new HashMap<String, TNodes>();
-        Set<Condition> leftConditions = new HashSet<Condition>();
-        SelectQuery leftQuery = create.selectQuery();
-
-        // the FROM and CONDITION are retrieved from the subquery
-/*
-        Table left = 

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