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| <h1 class="title">TDB Java API</h1> |
| |
| <p>All the operations of the |
| Jena API including the |
| <a href="../query/">SPARQL query and SPARQL Update</a> are supported. |
| The application obtains a model or RDF datasets from TDB then uses |
| it as for any other model or dataset.</p> |
| <h2 id="contents">Contents</h2> |
| <ul> |
| <li><a href="#constructing-a-model-or-dataset">Constructing a model or dataset</a> |
| <ul> |
| <li><a href="#using-a-directory-name">Using a directory name</a></li> |
| <li><a href="#using-an-assembler-file">Using an assembler file</a></li> |
| </ul> |
| </li> |
| <li><a href="#bulkloader">Bulkloader</a></li> |
| <li><a href="#concurrency">Concurrency</a></li> |
| <li><a href="#caching-and-synchronization">Caching and synchronization</a></li> |
| </ul> |
| <p>TDB also supports <a href="tdb_transactions.html">transactions</a>.</p> |
| <h2 id="constructing-a-model-or-dataset">Constructing a model or dataset</h2> |
| <p>The class <code>TDBFactory</code> contains the static factory methods for |
| creating and connecting to a TDB-backed graph or an RDF dataset. |
| Models and datasets should be closed after use.</p> |
| <p>An application can specify the model or dataset by:</p> |
| <ol> |
| <li>Giving a directory name</li> |
| <li>Giving an assembler file</li> |
| </ol> |
| <p>If a directory is empty, the TDB files for indexes and node table |
| are created. If the directory contains files from a previous |
| application run, TDB connects to the data already there.</p> |
| <p>Closing the model or dataset is important. Any updates made are |
| forced to disk if they have not been written already.</p> |
| <h3 id="using-a-directory-name">Using a directory name</h3> |
| <pre><code> // Make a TDB-backed dataset |
| String directory = "MyDatabases/Dataset1" ; |
| Dataset dataset = TDBFactory.createDataset(directory) ; |
| ... |
| dataset.begin(ReadWrite.READ) ; |
| // Get model inside the transaction |
| Model model = dataset.getDefaultModel() ; |
| dataset.end() ; |
| ... |
| dataset.begin(ReadWrite.WRITE) ; |
| model = dataset.getDefaultModel() ; |
| dataset.end() ; |
| ... |
| </code></pre> |
| <h3 id="using-an-assembler-file">Using an assembler file</h3> |
| <pre><code> // Assembler way: Make a TDB-back Jena model in the named directory. |
| // This way, you can change the model being used without changing the code. |
| // The assembler file is a configuration file. |
| // The same assembler description will work in Fuseki. |
| String assemblerFile = "Store/tdb-assembler.ttl" ; |
| Dataset dataset = TDBFactory.assembleDataset(assemblerFile) ; |
| ... |
| dataset.begin(ReadWrite.READ) ; |
| // Get model inside the transaction |
| Model model = dataset.getDefaultModel() ; |
| dataset.end() ; |
| ... |
| </code></pre> |
| <p>See |
| <a href="assembler.html">the TDB assembler documentation</a> |
| for details.</p> |
| <h2 id="bulkloader">Bulkloader</h2> |
| <p>The bulkloader is a faster way to load data into an empty dataset |
| than just using the Jena update operations.</p> |
| <p>It is accessed through the command line utility <code>tdbloader</code>.</p> |
| <h2 id="concurrency">Concurrency</h2> |
| <p>TDB support <a href="tdb_transactions.html">transactions</a>, which is the preferred |
| way to work. It is possible to act directly on the dataset without transaction |
| with a Multiple Reader or Single Writer (MRSW) policy for |
| concurrency access. Applications are expected to adhere to this |
| policy - it is not automatically checked.</p> |
| <p>One gotcha is Java iterators. An iterator that is moving over the |
| database is making read operations and no updates to the dataset |
| are possible while an iterator is being used.</p> |
| <h2 id="caching-and-synchronization">Caching and synchronization</h2> |
| <p>If used non-transactionally, then the application must be aware of |
| the caching and synchronization used by TDB. TDB employs caching at |
| various levels, from RDF terms to disk |
| blocks. It is important to flush all caches to make the file state |
| consistent with the cached states because some caches are |
| write-behind so unwritten changes may be held in-memory.</p> |
| <p>TDB provides an explicit call dataset objects for |
| synchronization with disk:</p> |
| <pre><code> Dataset dataset = ... ; |
| TDB.sync(dataset ) ; |
| </code></pre> |
| <p>Any dataset or model can be passed to these functions - if they are |
| not backed by TDB then no action is taken and the call merely |
| returns without error.</p> |
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