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| <h1 class="title">CSV PropertyTable - Implementation</h1> |
| |
| <h2 id="propertytable-implementations">PropertyTable Implementations</h2> |
| <p>There are 2 implementations for <code>PropertyTable</code>. The pros and cons are summarised in the following table:</p> |
| <table> |
| <thead> |
| <tr> |
| <th>PropertyTable Implementation</th> |
| <th>Description</th> |
| <th>Supported Indexes</th> |
| <th>Advantages</th> |
| <th>Disadvantages</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td><code>PropertyTableArrayImpl</code></td> |
| <td>implemented by a two-dimensioned Java array of <code>Nodes</code></td> |
| <td>SPO, PSO</td> |
| <td>compact memory usage, fast for querying with S and P, fast for query a whole <code>Row</code></td> |
| <td>slow for query with O, table Row/Column size provided</td> |
| </tr> |
| <tr> |
| <td><code>PropertyTableHashMapImpl</code></td> |
| <td>implemented by several Java <code>HashMaps</code></td> |
| <td>PSO, POS</td> |
| <td>fast for querying with O, table Row/Column size not required</td> |
| <td>more memory usage for HashMaps</td> |
| </tr> |
| </tbody> |
| </table> |
| <p>By default, [PropertyTableArrayImpl]((<a href="https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/PropertyTableArrayImpl.java">https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/PropertyTableArrayImpl.java</a>) is used as the <code>PropertyTable</code> implementation held by <code>GraphCSV</code>. |
| If you want to switch to <a href="https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/PropertyTableHashMapImpl.java">PropertyTableHashMapImpl</a>, just use the static method of <code>GraphCSV.createHashMapImpl()</code> to replace the default <code>new GraphCSV()</code> way. |
| Here is an example:</p> |
| <pre><code>Model model_csv_array_impl = ModelFactory.createModelForGraph(new GraphCSV(file)); // PropertyTableArrayImpl |
| Model model_csv_hashmap_impl = ModelFactory.createModelForGraph(GraphCSV.createHashMapImpl(file)); // PropertyTableHashMapImpl |
| </code></pre> |
| <h2 id="stagegenerator-optimization-for-graphpropertytable">StageGenerator Optimization for GraphPropertyTable</h2> |
| <p>Accessing from SPARQL via <code>Graph.find()</code> will work, but it’s not ideal. Some optimizations can be done for processing a SPARQL basic graph pattern. More explicitly, in the method of <code>OpExecutor.execute(OpBGP, ...)</code>, when the target for the query is a <code>GraphPropertyTable</code>, it can get a whole <code>Row</code>, or <code>Rows</code>, of the table data and match the pattern with the bindings.</p> |
| <p>The optimization of querying a whole <code>Row</code> in the PropertyTable are supported now. |
| The following query pattern can be transformed into a <code>Row</code> querying, without generating triples:</p> |
| <pre><code>?x :prop1 ?v . |
| ?x :prop2 ?w . |
| ... |
| </code></pre> |
| <p>It’s made by using the extension point of <code>StageGenerator</code>, because it’s now just concerned with <code>BasicPattern</code>. |
| The detailed workflow goes in this way:</p> |
| <ol> |
| <li>Split the incoming <code>BasicPattern</code> by subjects, (i.e. it becomes multiple sub BasicPatterns grouped by the same subjects. (see <a href="https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/QueryIterPropertyTable.java">QueryIterPropertyTable</a> )</li> |
| <li>For each sub <code>BasicPattern</code>, if the <code>Triple</code> size within is greater than 1 (i.e. at least 2 <code>Triples</code>), it’s turned into a <code>Row</code> querying, and processed by <a href="https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/QueryIterPropertyTableRow.java">QueryIterPropertyTableRow</a>, else if it contains only 1 <code>Triple</code>, it goes for the traditional <code>Triple</code> querying by <code>graph.graphBaseFind()</code></li> |
| </ol> |
| <p>In order to turn on this optimization, we need to register the <a href="https://github.com/apache/jena/tree/main/jena-csv/src/main/java/org/apache/jena/propertytable/impl/StageGeneratorPropertyTable.java">StageGeneratorPropertyTable</a> into ARQ context, before performing SPARQL querying:</p> |
| <pre><code>StageGenerator orig = (StageGenerator)ARQ.getContext().get(ARQ.stageGenerator) ; |
| StageGenerator stageGenerator = new StageGeneratorPropertyTable(orig) ; |
| StageBuilder.setGenerator(ARQ.getContext(), stageGenerator) ; |
| </code></pre> |
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