TDB Java API
All the operations of the Jena API including the SPARQL query and SPARQL Update are supported. The application obtains a model or RDF datasets from TDB then uses it as for any other model or dataset.
- Constructing a model or dataset
- Caching and synchronization
TDB also supports transactions.
Constructing a model or dataset
TDBFactory 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.
An application can specify the model or dataset by:
- Giving a directory name
- Giving an assembler file
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.
Closing the model or dataset is important. Any updates made are forced to disk if they have not been written already.
Using a directory name
// Direct way: Make a TDB-backed Jena model in the named directory. String directory = "MyDatabases/DB1" ; Model model = TDBFactory.createModel(directory) ; ... model.close() ; // Direct way: Make a TDB-backed dataset String directory = "MyDatabases/Dataset1" ; Dataset dataset = TDBFactory.createDataset(directory) ; ... dataset.close() ;
Using an assembler file
// 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" ; Model model = TDBFactory.assembleModel(assemblerFile) ; ... model.close() ; String assemblerFile = "Store/tdb-assembler.ttl" ; Dataset dataset = TDBFactory.assembleDataset(assemblerFile) ; ... dataset.close() ;
See the TDB assembler documentation for details.
The bulkloader is a faster way to load data into an empty graph than just using the Jena update operations.
It is accessed through the command line utility
TDB support transactions, 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.
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.
Caching and synchronization
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.
TDB provides an explicit call for model and dataset objects for synchronization with disk:
Model model = ... ; TDB.sync(model) ; Dataset dataset = ... ; TDB.sync(dataset ) ;
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.