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Posted to commits@jena.apache.org by bu...@apache.org on 2016/12/23 17:50:35 UTC
svn commit: r1003354 - in /websites/staging/jena/trunk/content: ./
documentation/notes/rdfconnection.html
Author: buildbot
Date: Fri Dec 23 17:50:34 2016
New Revision: 1003354
Log:
Staging update by buildbot for jena
Added:
websites/staging/jena/trunk/content/documentation/notes/rdfconnection.html
Modified:
websites/staging/jena/trunk/content/ (props changed)
Propchange: websites/staging/jena/trunk/content/
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@@ -0,0 +1,367 @@
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+ <h1 class="title">RDF Connection : SPARQL operations API</h1>
+ <style type="text/css">
+/* The following code is added by mdx_elementid.py
+ It was originally lifted from http://subversion.apache.org/style/site.css */
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+<p><code>RDFConnection</code> provides a unified set of operations for working on RDF
+with SPARQL operations. It provides <a
+href="http://www.w3.org/TR/sparql11-query/">SPARQL Query</a>, <a
+href="http://www.w3.org/TR/sparql11-update/">SPARQL Update</a> and the <a
+href="http://www.w3.org/TR/sparql11-http-rdf-update/">SPARQL Graph
+Store</a> operations. The interface is uniform - the same interface
+applies to local data and to remote data using HTTP and the SPARQL
+protocols ( <a href="http://www.w3.org/TR/sparql11-protocol/">SPARQL
+protocol</a> and <a
+href="http://www.w3.org/TR/sparql11-http-rdf-update/">SPARQL Graph Store
+Protocol</a>).</p>
+<h2 id="outline">Outline<a class="headerlink" href="#outline" title="Permanent link">¶</a></h2>
+<p><code>RDFConnection</code> provides a number of different styles for working with RDF
+data in Java. It provides support for try-resource and functional code
+passing styles, as well the more basic sequence of methods calls.</p>
+<p>For example: using <code>try-resources</code> to manage the connection, and perform two operations, one to load
+some data, and one to make a query can be written as:</p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="p">(</span> <span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(...)</span> <span class="p">)</span> <span class="p">{</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">querySelect</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="n">DISTINCT</span> ?<span class="n">s</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">,</span> <span class="p">(</span><span class="n">qs</span><span class="p">)</span><span class="o">-></span>
+ <span class="n">Resource</span> <span class="n">subject</span> <span class="p">=</span> <span class="n">qs</span><span class="p">.</span><span class="n">getResource</span><span class="p">(</span>"<span class="n">s</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">System</span><span class="p">.</span><span class="n">out</span><span class="p">.</span><span class="n">println</span><span class="p">(</span>"<span class="n">Subject</span><span class="p">:</span> "<span class="o">+</span><span class="n">subject</span><span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>This could have been written as (approximately -- the error handling is better
+in the example above):</p>
+<div class="codehilite"><pre><span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(...)</span>
+<span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+<span class="n">QueryExecution</span> <span class="n">qExec</span> <span class="p">=</span> <span class="n">conn</span><span class="p">.</span><span class="n">query</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="n">DISTINCT</span> ?<span class="n">s</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">)</span> <span class="p">;</span>
+<span class="n">ResultSet</span> <span class="n">rs</span> <span class="p">=</span> <span class="n">qExec</span><span class="p">.</span><span class="n">execSelect</span><span class="p">()</span> <span class="p">;</span>
+<span class="k">while</span><span class="p">(</span><span class="n">rs</span><span class="p">.</span><span class="n">hasNext</span><span class="p">())</span> <span class="p">{</span>
+ <span class="n">QuerySolution</span> <span class="n">qs</span> <span class="p">=</span> <span class="n">rs</span><span class="p">.</span><span class="n">next</span><span class="p">()</span> <span class="p">;</span>
+ <span class="n">Resource</span> <span class="n">subject</span> <span class="p">=</span> <span class="n">qs</span><span class="p">.</span><span class="n">getResource</span><span class="p">(</span>"<span class="n">s</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">System</span><span class="p">.</span><span class="n">out</span><span class="p">.</span><span class="n">println</span><span class="p">(</span>"<span class="n">Subject</span><span class="p">:</span> "<span class="o">+</span><span class="n">subject</span><span class="p">)</span> <span class="p">;</span>
+<span class="p">}</span>
+<span class="n">qExec</span><span class="p">.</span><span class="n">close</span><span class="p">()</span> <span class="p">;</span>
+<span class="n">conn</span><span class="p">.</span><span class="n">close</span><span class="p">()</span> <span class="p">;</span>
+</pre></div>
+
+
+<p>Jena also provides a separate
+<a href="http://jena.staging.apache.org/documentation/jdbc/index.html">SPARQL over JDBC driver</a>
+library.</p>
+<h2 id="transactions">Transactions<a class="headerlink" href="#transactions" title="Permanent link">¶</a></h2>
+<p>Transactions are the preferred way to work with RDF data.
+Operations on an <code>RDFConnection</code> outside of an application-controlled
+transaction will cause the system to add one for the duration of the
+operation. This "autocommit" feature may lead to inefficient operations due
+to excessive overhead.</p>
+<p>The <code>Txn</code> class provides a Java8-style transaction API. Transactions are
+code passed in the <code>Txn</code> library that handles the transaction lifecycle.</p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="p">(</span> <span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(...)</span> <span class="p">)</span> <span class="p">{</span>
+ <span class="n">Txn</span><span class="p">.</span><span class="n">execWrite</span><span class="p">(</span><span class="n">conn</span><span class="p">,</span> <span class="p">()</span><span class="o">-></span> <span class="p">{</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data1</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data2</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">querySelect</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="n">DISTINCT</span> ?<span class="n">s</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">,</span> <span class="p">(</span><span class="n">qs</span><span class="p">)</span><span class="o">-></span>
+ <span class="n">Resource</span> <span class="n">subject</span> <span class="p">=</span> <span class="n">qs</span><span class="p">.</span><span class="n">getResource</span><span class="p">(</span>"<span class="n">s</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">System</span><span class="p">.</span><span class="n">out</span><span class="p">.</span><span class="n">println</span><span class="p">(</span>"<span class="n">Subject</span><span class="p">:</span> "<span class="o">+</span><span class="n">subject</span><span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>The traditional style of explicit <code>begin</code>, <code>commit</code>, <code>abort</code> is also available.</p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="p">(</span> <span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(...)</span> <span class="p">)</span> <span class="p">{</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">begin</span><span class="p">(</span><span class="n">ReadWrite</span><span class="p">.</span><span class="n">WRITE</span><span class="p">)</span> <span class="p">;</span>
+ <span class="k">try</span> <span class="p">{</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data1</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data2</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">querySelect</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="n">DISTINCT</span> ?<span class="n">s</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">,</span> <span class="p">(</span><span class="n">qs</span><span class="p">)</span><span class="o">-></span>
+ <span class="n">Resource</span> <span class="n">subject</span> <span class="p">=</span> <span class="n">qs</span><span class="p">.</span><span class="n">getResource</span><span class="p">(</span>"<span class="n">s</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">System</span><span class="p">.</span><span class="n">out</span><span class="p">.</span><span class="n">println</span><span class="p">(</span>"<span class="n">Subject</span><span class="p">:</span> "<span class="o">+</span><span class="n">subject</span><span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">commit</span><span class="p">()</span> <span class="p">;</span>
+ <span class="p">}</span> <span class="n">finally</span> <span class="p">{</span> <span class="n">conn</span><span class="p">.</span><span class="k">end</span><span class="p">()</span> <span class="p">;</span> <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>The use of <code>try-finally</code> ensures that transactions are properly finished.
+The <code>conn.end()</code> provides an abort in case an exception occurs in the
+transaction and a commit has not been issued. The use of <code>try-finally</code>
+ensures that transactions are properly finished.</p>
+<p><code>Txn</code> is wrapping these steps up and calling the application supplied code
+for the transaction body.</p>
+<h3 id="remote-transactions">Remote Transactions<a class="headerlink" href="#remote-transactions" title="Permanent link">¶</a></h3>
+<p>SPARQL does not define a remote transaction standard protocol. Each remote
+operation shuld be atomic (all happens or nothing happens) - this is the
+responsibility of the remote server.</p>
+<p>An <code>RDFConnection</code> will at least provide the client-side locking features.
+This means that overlapping operations that change data are naturally
+handled by the transaction pattern within a single JVM.</p>
+<h2 id="graph-store-protocol">Graph Store Protocol<a class="headerlink" href="#graph-store-protocol" title="Permanent link">¶</a></h2>
+<p>The <a href="http://www.w3.org/TR/sparql11-http-rdf-update/">SPARQL Graph
+Store Protocol</a> (GSP) is a set of operations to work on whole graphs in a
+dataset. It provides a standardised way to manage the data in a dataset.</p>
+<p>The operations are to fetch a graph, set the RDF data in a graph,
+add more RDF data into a graph, and delete a graph from a dataset.</p>
+<p>For example: load two files:
+ try ( RDFConnection conn = RDFConnectionFactory.connect(...) ) {
+ conn.load("data1.ttl") ;
+ conn.load("data2.nt") ;
+ } </p>
+<p>The file extension is used to determine the syntax.</p>
+<p>There is also a set of scripts to help do these operations from the command
+line with <a href="http://jena.apache.org/documentation/fuseki2/soh.html"</p>
+<blockquote>
+<p>SOH</a>. It is possible to write curl scripts as well. The SPARQL Graph
+Store Protocol provides a standardised way to manage the data in a dataset.</p>
+</blockquote>
+<p>In addition, <code>RDFConnection</code> provides an extension to give the same style
+of operation to work on a whole dataset (deleting the dataset is not
+provided).</p>
+<div class="codehilite"><pre><span class="n">conn</span><span class="p">.</span><span class="n">loadDataset</span><span class="p">(</span>"<span class="n">data</span><span class="o">-</span><span class="n">complete</span><span class="p">.</span><span class="n">trig</span>"<span class="p">)</span> <span class="p">;</span>
+</pre></div>
+
+
+<h3 id="local-vs-remote">Local vs Remote<a class="headerlink" href="#local-vs-remote" title="Permanent link">¶</a></h3>
+<p>GSP operations work on while models and datasets. When used on a remote connection,
+the result of a GSP operation is a separate copy of the remote RDF data. When working
+with local connections, 3 isolations modes are available:</p>
+<ul>
+<li>Copy – the models and datasets returned are independent copies.
+Updates are made to the return copy only. This is most like
+a remote connectionand is useful for testing.</li>
+<li>Read-only – the models and datasets are made read-only but any changes
+to the underlying RDF data by changes by another route will be visible.
+This provides a form of checking for large datasets when "copy" is impractical.</li>
+<li>None – the models and datasets are passed back with no additional wrappers
+and they can be updated with the changes being made the underlying dataset.</li>
+</ul>
+<p>The default for a local <code>RDFConnection</code> is "none". </p>
+<h2 id="query-usage">Query Usage<a class="headerlink" href="#query-usage" title="Permanent link">¶</a></h2>
+<p><code>RDFConnection</code> provides methods for each of the SPARQL query forms (<code>SELECT</code>,
+<code>CONSTRUCT</code>, <code>DESCRIBE</code>, <code>ASK</code>) as well as a way to get the lower level
+<code>QueryExecution</code> for specialized configuration.</p>
+<p>When creating an <code>QueryExecution</code> explicitly, care shoud be taken to close
+it. If the application wishes to capture the result set from a SELECT query and
+retain it across the lifetime of the transaction or <code>QueryExecution</code>, then
+the application should create a copy which is not attached to any external system
+with <code>ResultSetFactory.copyResults</code>.</p>
+<div class="codehilite"><pre> <span class="k">try</span> <span class="p">(</span> <span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(</span>"<span class="n">foo</span>"<span class="p">)</span> <span class="p">)</span> <span class="p">{</span>
+ <span class="n">ResultSet</span> <span class="n">safeCopy</span> <span class="p">=</span>
+ <span class="n">Txn</span><span class="p">.</span><span class="n">execReadReturn</span><span class="p">(</span><span class="n">conn</span><span class="p">,</span> <span class="p">()</span><span class="o">-></span> <span class="p">{</span>
+ <span class="o">//</span> <span class="n">Process</span> <span class="n">results</span> <span class="n">by</span> <span class="n">row</span><span class="p">:</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">querySelect</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="n">DISTINCT</span> ?<span class="n">s</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">,</span> <span class="p">(</span><span class="n">qs</span><span class="p">)</span><span class="o">-></span><span class="p">{</span>
+ <span class="n">Resource</span> <span class="n">subject</span> <span class="p">=</span> <span class="n">qs</span><span class="p">.</span><span class="n">getResource</span><span class="p">(</span>"<span class="n">s</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="n">System</span><span class="p">.</span><span class="n">out</span><span class="p">.</span><span class="n">println</span><span class="p">(</span>"<span class="n">Subject</span><span class="p">:</span> "<span class="o">+</span><span class="n">subject</span><span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+ <span class="n">ResultSet</span> <span class="n">rs</span> <span class="p">=</span> <span class="n">conn</span><span class="p">.</span><span class="n">query</span><span class="p">(</span>"<span class="n">SELECT</span> <span class="o">*</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span>"<span class="p">).</span><span class="n">execSelect</span><span class="p">()</span> <span class="p">;</span>
+ <span class="k">return</span> <span class="n">ResultSetFactory</span><span class="p">.</span><span class="n">copyResults</span><span class="p">(</span><span class="n">rs</span><span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+ <span class="p">}</span>
+</pre></div>
+
+
+<h2 id="update-usage">Update Usage<a class="headerlink" href="#update-usage" title="Permanent link">¶</a></h2>
+<p>SPARQL Update opertions can be performed and mixed with other operations.</p>
+<div class="codehilite"><pre> <span class="k">try</span> <span class="p">(</span> <span class="n">RDFConnection</span> <span class="n">conn</span> <span class="p">=</span> <span class="n">RDFConnectionFactory</span><span class="p">.</span><span class="n">connect</span><span class="p">(...)</span> <span class="p">)</span> <span class="p">{</span>
+ <span class="n">Txn</span><span class="p">.</span><span class="n">execWrite</span><span class="p">(</span><span class="n">conn</span><span class="p">,</span> <span class="p">()</span><span class="o">-></span> <span class="p">{</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">update</span><span class="p">(</span>"<span class="n">DELETE</span> <span class="n">DATA</span> <span class="p">{</span> <span class="p">...</span> <span class="p">}</span>" <span class="p">)</span> <span class="p">;</span>
+ <span class="n">conn</span><span class="p">.</span><span class="n">load</span><span class="p">(</span>"<span class="n">data</span><span class="p">.</span><span class="n">ttl</span>"<span class="p">)</span> <span class="p">;</span>
+ <span class="p">})</span> <span class="p">;</span>
+</pre></div>
+
+
+<h2 id="dataset-operations">Dataset operations<a class="headerlink" href="#dataset-operations" title="Permanent link">¶</a></h2>
+<p>In addition to the SPARQL Graph Store Protocol, operations on whole
+datasets are provided for fetching (HTTP GET), adding data (HTTP POST) and
+setting the data (HTTP PUT) on a dataset URL. This assumes the remote
+server supported these REST-style operations. Apache Jena Fuseki does
+provide these.</p>
+<h2 id="subinterfaces">Subinterfaces<a class="headerlink" href="#subinterfaces" title="Permanent link">¶</a></h2>
+<p>To help structure code, the <code>RDFConnection</code> consists of a number of
+different interfaces. An <code>RDFConnection</code> can be passed to application code
+as one of these interfaces so that only certain subsets of the full
+operations are visible to the called code.</p>
+<ul>
+<li>query via <code>SparqlQueryConnection</code></li>
+<li>update via <code>SparqlUpdateConnection</code></li>
+<li>graph store protocol <code>RDFDatasetAccessConnection</code> (read operations),
+ and <code>RDFDatasetConnection</code> (read and write operations).</li>
+</ul>
+<h2 id="examples">Examples<a class="headerlink" href="#examples" title="Permanent link">¶</a></h2>
+<p>See
+https://github.com/apache/jena/tree/master/jena-rdfconnection/src/main/java/rdfconnection/examples</p>
+ </div>
+</div>
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