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| <h1 class="title">SDB JavaAPI</h1> |
| |
| <p>This page describes how to use SDB from Java.</p> |
| <p>Code examples are in <code>src-examples/</code> in the SDB distribution.</p> |
| <h2 id="contents">Contents</h2> |
| <ul> |
| <li><a href="#concepts">Concepts</a></li> |
| <li><a href="#obtaining-the-store">Obtaining the Store</a> |
| <ul> |
| <li><a href="#from-a-configuration-file">From a configuration file</a></li> |
| <li><a href="#in-java-code">In Java code</a></li> |
| <li><a href="#database-user-and-password">Database User and Password</a></li> |
| </ul> |
| </li> |
| <li><a href="#connection-management">Connection Management</a></li> |
| <li><a href="#formatting-or-emptying-the-store">Formatting or Emptying the Store</a></li> |
| <li><a href="#loading-data">Loading data</a></li> |
| <li><a href="#executing-queries">Executing Queries</a></li> |
| <li><a href="#using-the-jena-model-api-with-sdb">Using the Jena Model API with SDB</a></li> |
| </ul> |
| <h2 id="concepts">Concepts</h2> |
| <ul> |
| <li><code>Store</code></li> |
| <li><code>SDBFactory</code></li> |
| <li><code>SDBConnection</code></li> |
| </ul> |
| <p>SDB loads and queries data based on the unit of a <code>Store</code>. The |
| <code>Store</code> object has all the information for formatting, loading and |
| accessing an SDB database. One database or table space is one |
| Store. <code>Store</code> objects are made via the static method of the |
| <code>StoreFactory</code> class.</p> |
| <p><code>SDBConnection</code> wraps the underlying database connection, as well |
| as providing logging operations.</p> |
| <ul> |
| <li><code>StoreDesc</code></li> |
| </ul> |
| <p>A store description is the low level mechanism for describing |
| stores to be created.</p> |
| <ul> |
| <li><code>DatasetStore</code></li> |
| <li><code>GraphSDB</code></li> |
| </ul> |
| <p>Two further class are not immediately visible because they are |
| managed by the <code>SDBFactory</code> which creates the necessary classes, |
| such as Jena models and graphs.</p> |
| <p>An object of class <code>DatasetStore</code> represents an |
| <a href="http://www.w3.org/TR/sparql11-query/#rdfDataset" title="http://www.w3.org/TR/rdf-sparql-query/#rdfDataset">RDF dataset</a> |
| backed by an SDB store. Objects of this class trigger SPARQL |
| queries being sent to SDB.</p> |
| <p>The class <code>GraphSDB</code> provides the adapter between the standard Jena |
| Java API and an SDB store, either to the default graph or one of |
| the named graphs. The <code>SDBFactory</code> can also create Jena Models |
| backed by such a graph.</p> |
| <h2 id="obtaining-the-store">Obtaining the Store</h2> |
| <p>A store is build from a description. This can be a description in |
| file as a |
| <a href="../assembler">Jena assembler</a> |
| or the application can build the store description |
| programmatically.</p> |
| <h3 id="from-a-configuration-file">From a configuration file</h3> |
| <p>The stored description is the only point where the specific details |
| of store are given. This includes connection information, the |
| database name, and database type. It makes sense to place this |
| outside the code. That way, the application can be switched between |
| different databases (e.g. testing and production) by changing a |
| configuration file, and not the code, which would require |
| recompilation and a rebuild.</p> |
| <p>To create a <code>Store</code> from a store assembler</p> |
| <pre><code> Store store = SDBFactory.connectStore("sdb.ttl") ; |
| </code></pre> |
| <p>The assembler file has two parts, the connection details and the |
| store type.</p> |
| <pre><code> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . |
| @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . |
| @prefix ja: <http://jena.hpl.hp.com/2005/11/Assembler#> . |
| @prefix sdb: <http://jena.hpl.hp.com/2007/sdb#> . |
| |
| _:c rdf:type sdb:SDBConnection ; |
| sdb:sdbType "derby" ; |
| sdb:sdbName "DB/SDB2" ; |
| sdb:driver "org.apache.derby.jdbc.EmbeddedDriver" ; |
| . |
| |
| [] rdf:type sdb:Store ; |
| sdb:layout "layout2" ; |
| sdb:connection _:c ; |
| . |
| </code></pre> |
| <p>See the full details of |
| <a href="store_description.html" title="SDB/Store Description">store description files</a> |
| for the options.</p> |
| <h3 id="in-java-code">In Java code</h3> |
| <p>The less flexible way to create a store description is to build it |
| in Java. For example:</p> |
| <pre><code> StoreDesc storeDesc = new StoreDesc(LayoutType.LayoutTripleNodesHash, |
| DatabaseType.Derby) ; |
| JDBC.loadDriverDerby() ; |
| String jdbcURL = "jdbc:derby:DB/SDB2"; |
| SDBConnection conn = new SDBConnection(jdbcURL, null, null) ; |
| Store store = SDBFactory.connectStore(conn, storeDesc) ; |
| </code></pre> |
| <h3 id="database-user-and-password">Database User and Password</h3> |
| <p>The user and password for the database can be set in explicitly in |
| the description file but it is usually better to use an environment |
| variable or Java system property because this avoid writing use and |
| password in a file.</p> |
| <p>Environment variable: <code>SDB_USER</code> |
| Java property: <code>jena.db.user</code></p> |
| <p>Environment variable: <code>SDB_PASSWORD</code> |
| Java property: <code>jena.db.password</code></p> |
| <h2 id="connection-management">Connection Management</h2> |
| <p>Each store has a JDBC connection associated with it.</p> |
| <p>In situations where such connections are managed externally, the |
| store object can be created and used within a single operation.</p> |
| <p>A <code>Store</code> is lightweight and does not perform any database actions |
| when created, so creating and releasing them will not impact |
| performance. Closing a store does not close the JDBC connection.</p> |
| <p>Similarly, a <code>SDBConnection</code> is lightweight and creation does not |
| result in any database or JDBC connection actions.</p> |
| <p>The store description can be read from the same file because any |
| SDB connection information is ignored when reading to get just the |
| store description. The store description can be kept across store |
| creations:</p> |
| <pre><code> storeDesc = StoreDesc.read("sdb.ttl") ; |
| </code></pre> |
| <p>then used with an JDBC connection object passed from the connection |
| container:</p> |
| <pre><code> public static void query(String queryString, |
| StoreDesc storeDesc, |
| Connection jdbcConnection) |
| { |
| Query query = QueryFactory.create(queryString) ; |
| |
| SDBConnection conn = SDBFactory.createConnection(jdbcConnection) ; |
| |
| Store store = SDBFactory.connectStore(conn, storeDesc) ; |
| |
| Dataset ds = SDBFactory.connectDataset(store) ; |
| try(QueryExecution qe = QueryExecutionFactory.create(query, ds)) { |
| ResultSet rs = qe.execSelect() ; |
| ResultSetFormatter.out(rs) ; |
| } |
| store.close() ; |
| } |
| </code></pre> |
| <h2 id="formatting-or-emptying-the-store">Formatting or Emptying the Store</h2> |
| <p>SDB stores do not ensure that the database is formatted. You can |
| check whether the store is already formatted using:</p> |
| <pre><code>StoreUtils.isFormatted(store); |
| </code></pre> |
| <p>This is an expensive operation, and should be used sparingly.</p> |
| <p>Once you obtain a store for the first time you will need to:</p> |
| <pre><code>store.getTableFormatter().create(); |
| </code></pre> |
| <p>This will create the necessary tables and indexes required for a |
| full SDB store.</p> |
| <p>You may empty the store completely using:</p> |
| <pre><code>store.getTableFormatter().truncate(); |
| </code></pre> |
| <h2 id="loading-data">Loading data</h2> |
| <p>Data loading uses the standard Jena <code>Model.read</code> operations. |
| <code>GraphSDB</code>, and models made from a <code>GraphSDB</code>, implement the |
| standard Jena bulk data interface with backed by an SBD |
| implementation of that interface.</p> |
| <h2 id="executing-queries">Executing Queries</h2> |
| <p>The interface to making queries with SDB is same as that for |
| <a href="../query/app_api.html">querying with ARQ</a>. |
| SDB is an ARQ query engine that can handle queries made on an RDF |
| dataset which is of the SDB class <code>DatasetStore</code>:</p> |
| <pre><code> Dataset ds = DatasetStore.create(store) ; |
| </code></pre> |
| <p>This is then used as normal with ARQ:</p> |
| <pre><code> Dataset ds = DatasetStore.create(store) ; |
| try(QueryExecution qe = QueryExecutionFactory.create(query, ds)) { |
| ResultSet rs = qe.execSelect() ; |
| ResultSetFormatter.out(rs) ; |
| } |
| </code></pre> |
| <p>When finished, the store should be closed to release any resources |
| associated with the particular implementation. Closing a store does |
| <em>not</em> close it’s JDBC connection.</p> |
| <pre><code> store.close() ; |
| </code></pre> |
| <p>Closing the SDBConnection <em>does</em> close the JDBC connection:</p> |
| <pre><code> store.getConnection().close() ; |
| store.close() ; |
| </code></pre> |
| <p>If models or graphs backed by SDB are placed in a general Dataset |
| then the query is not efficiently executed by SDB.</p> |
| <h2 id="using-the-jena-model-api-with-sdb">Using the Jena Model API with SDB</h2> |
| <p>A Jena model can be connected to one graph in the store and used |
| with all the Jena API operations.</p> |
| <p>Here, the graph for the model is the default graph:</p> |
| <pre><code> Store store = SDBFactory.connectStore("sdb.ttl") ; |
| Model model = SDBFactory.connectDefaultModel(store) ; |
| |
| StmtIterator sIter = model.listStatements() ; |
| for ( ; sIter.hasNext() ; ) |
| { |
| Statement stmt = sIter.nextStatement() ; |
| System.out.println(stmt) ; |
| } |
| sIter.close() ; |
| store.close() ; |
| </code></pre> |
| <p>SDB is optimized for SPARQL queries but queries and other Jena API |
| operations can be mixed. The results from a SPARQL query are Jena |
| RDFNodes, with the associated model having a graph implemented by |
| SDB.</p> |
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