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.. _persistence: Persistence
===========
Persistence
===========
RDFLib provides an :class:`abstracted Store API <rdflib.store.Store>`
for persistence of RDF and Notation 3. The
:class:`~rdflib.graph.Graph` class works with instances of this API
(as the first argument to its constructor) for triple-based management
of an RDF store including: garbage collection, transaction management,
update, pattern matching, removal, length, and database management
(:meth:`~rdflib.graph.Graph.open` / :meth:`~rdflib.graph.Graph.close`
/ :meth:`~rdflib.graph.Graph.destroy`).
Additional persistence mechanisms can be supported by implementing
this API for a different store.
Stores currently shipped with core RDFLib
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
* :class:`Memory <rdflib.plugins.stores.memory.Memory>` - not persistent!
* :class:`~rdflib.plugins.stores.berkeleydb.BerkeleyDB` - on disk persistence via Python's `berkeleydb package <https://pypi.org/project/berkeleydb/>`_
* :class:`~rdflib.plugins.stores.sparqlstore.SPARQLStore` - a read-only wrapper around a remote SPARQL Query endpoint
* :class:`~rdflib.plugins.stores.sparqlstore.SPARQLUpdateStore` - a read-write wrapper around a remote SPARQL query/update endpoint pair
Usage
^^^^^
In most cases, passing the name of the store to the Graph constructor is enough:
.. code-block:: python
from rdflib import Graph
graph = Graph(store='BerkeleyDB')
Most stores offering on-disk persistence will need to be opened before reading or writing.
When peristing a triplestore, rather than a ConjuntiveGraph quadstore, you need to specify
an identifier with which you can open the graph:
.. code-block:: python
graph = Graph('BerkeleyDB', identifier='mygraph')
# first time create the store:
graph.open('/home/user/data/myRDFLibStore', create=True)
# work with the graph:
data = """
PREFIX : <https://example.org/>
:a :b :c .
:d :e :f .
:d :g :h .
"""
graph.parse(data=data, format="ttl")
# when done!
graph.close()
When done, :meth:`~rdflib.graph.Graph.close` must be called to free the resources associated with the store.
Additional store plugins
^^^^^^^^^^^^^^^^^^^^^^^^
More store implementations are available in RDFLib extension projects:
* `rdflib-sqlalchemy <https://github.com/RDFLib/rdflib-sqlalchemy>`_ – a store which supports a wide-variety of RDBMS backends,
* `rdflib-leveldb <https://github.com/RDFLib/rdflib-leveldb>`_ – a store on top of Google's `LevelDB <https://code.google.com/p/leveldb/>`_ key-value store.
* `rdflib-kyotocabinet <https://github.com/RDFLib/rdflib-kyotocabinet>`_ – a store on top of the `Kyoto Cabinet <http://fallabs.com/kyotocabinet/>`_ key-value store.
Example
^^^^^^^
* :mod:`examples.berkeleydb_example` contains an example for using a BerkeleyDB store.
* :mod:`examples.sparqlstore_example` contains an example for using a SPARQLStore.
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