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231 lines
6.8 KiB
231 lines
6.8 KiB
Oxigraph for Python
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===================
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[](https://github.com/oxigraph/oxigraph/actions)
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This package provides a Python API on top of Oxigraph.
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Oxigraph is a work in progress graph database written in Rust implementing the [SPARQL](https://www.w3.org/TR/sparql11-overview/) standard.
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It offers two stores with [SPARQL 1.1 Query](https://www.w3.org/TR/sparql11-query/) capabilities.
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One of the store is in-memory, and the other one is disk based.
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The store is also able to load RDF serialized in [Turtle](https://www.w3.org/TR/turtle/), [TriG](https://www.w3.org/TR/trig/), [N-Triples](https://www.w3.org/TR/n-triples/), [N-Quads](https://www.w3.org/TR/n-quads/) and [RDF XML](https://www.w3.org/TR/rdf-syntax-grammar/).
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## Install
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To install the development version of Oxigraph you need first to install the build tool [Maturin](https://github.com/PyO3/maturin).
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This could be done using the usual `pip install maturin`.
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Then you just need to run `maturin develop` to install Oxigraph in the current Python environment.
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## Example
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Insert the triple `<http://example/> <http://schema.org/name> "example"` and print the name of `<http://example/>` in SPARQL:
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```python
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from oxigraph import *
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store = MemoryStore()
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ex = NamedNode('http://example/')
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schemaName = NamedNode('http://schema.org/name')
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store.add((ex, schemaName, Literal('example')))
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for binding in store.query('SELECT ?name WHERE { <http://example/> <http://schema.org/name> ?name }'):
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print(binding['name'].value)
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```
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## API
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### Model
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Oxigraph provides python classes for the basic RDF model elements.
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#### `NamedNode`
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An RDF [IRI](https://www.w3.org/TR/rdf11-concepts/#dfn-iri).
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```python
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from oxigraph import NamedNode
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assert NamedNode('http://example.com/foo').value == 'http://example.com/foo'
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assert str(NamedNode('http://example.com/foo')) == '<http://example.com/foo>'
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```
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#### `BlankNode`
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An RDF [blank node](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node).
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```python
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from oxigraph import BlankNode
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assert BlankNode('foo').value == 'foo'
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assert str(BlankNode('foo')) == 'foo'
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```
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#### `Literal`
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An RDF [literal](https://www.w3.org/TR/rdf11-concepts/#dfn-literal).
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```python
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from oxigraph import NamedNode, Literal
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assert Literal('foo').value == 'foo'
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assert str(NamedNode('foo')) == '"foo"'
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assert Literal('foo', language='en').language == 'en'
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assert str(NamedNode('foo', language='en')) == '"foo"@en'
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assert Literal('11', datatype=NamedNode('http://www.w3.org/2001/XMLSchema#integer')).datatype == 'http://www.w3.org/2001/XMLSchema#integer'
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assert str(Literal('11', datatype=NamedNode('http://www.w3.org/2001/XMLSchema#integer'))) == '"foo"^^<http://www.w3.org/2001/XMLSchema#integer>'
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```
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#### `DefaultGraph`
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The RDF [default graph name](https://www.w3.org/TR/rdf11-concepts/#dfn-default-graph).
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```python
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from oxigraph import DefaultGraph
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DefaultGraph()
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```
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### Stores
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Oxigraph provides two stores:
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* `MemoryStore` that stores the RDF quads in memory
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* `SledStore` that stores the graph on disk using [Sled](https://github.com/spacejam/sled).
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Both stores provide a similar API. They encode an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
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#### Constructor
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##### `MemoryStore`
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It could be constructed using:
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```python
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from oxigraph import MemoryStore
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store = MemoryStore()
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```
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##### `SledStore`
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The following code creates a store using the directory `foo/bar` for storage.
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```python
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from oxigraph import SledStore
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store = SledStore('foo/bar')
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```
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It is also possible to use a temporary directory that will be removed when the `SledStore` Python object is dropped:
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```python
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from oxigraph import SledStore
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store = SledStore()
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```
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#### `add`
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To add a quad in the store:
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```python
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s = NamedNode('http://example.com/subject')
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p = NamedNode('http://example.com/predicate')
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o = NamedNode('http://example.com/object')
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g = NamedNode('http://example.com/graph')
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store.add((s, p, o, g))
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```
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If a triple is provided, it is added to the default graph i.e. `store.add((s, p, o, g))` is the same as `store.add((s, p, o, DefaultGraph()))`
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#### `remove`
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To remove a quad from the store:
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```python
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store.remove((s, p, o, g))
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```
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#### `__contains__`
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Checks if a quad is in the store:
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```python
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assert (s, p, o, g) in store
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```
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#### `__len__`
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Returns the number of quads in the store:
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```python
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assert len(store) == 1
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```
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#### `__iter__`
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Iterates on all quads in the store:
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```python
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assert list(iter(store)) == [(s, p, o, g)]
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```
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#### `match`
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Returns all the quads matching a given pattern using an iterator.
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Return all the quads with the subject `s`:
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```python
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assert list(store.match(s, None, None, None)) == [(s, p, o, g)]
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```
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Return all the quads in the default graph:
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```python
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assert list(store.match(s, None, None, DefaultGraph())) == []
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```
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#### `query`
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Executes a [SPARQL 1.1 Query](https://www.w3.org/TR/sparql11-query/).
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The `ASK` queries return a boolean:
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```python
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assert store.query('ASK { ?s ?s ?s }')
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```
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The `SELECT` queries return an iterator of query solutions that could be indexed by variable name or position in the `SELECT` clause:
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```python
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for solution in store.query('SELECT ?s WHERE { ?s ?p ?o }'):
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assert solution[0] == solution['s']
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```
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The `CONSTRUCT` and `DESCRIBE` queries return an iterator of triples:
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```python
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for (s, p, o) in store.query('CONSTRUCT { ?s ?p ?o } WHERE { ?s ?p ?o }'):
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print(s)
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```
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### `load`
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Loads serialized RDF triples or quad into the store.
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The method arguments are:
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1. `data`: the serialized RDF triples or quads.
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2. `mime_type`: the MIME type of the serialization. See below for the supported mime types.
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3. `base_iri`: the base IRI used to resolve the relative IRIs in the serialization.
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4. `to_named_graph`: for triple serialization formats, the name of the named graph the triple should be loaded to.
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The available formats are:
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* [Turtle](https://www.w3.org/TR/turtle/): `text/turtle`
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* [TriG](https://www.w3.org/TR/trig/): `application/trig`
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* [N-Triples](https://www.w3.org/TR/n-triples/): `application/n-triples`
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* [N-Quads](https://www.w3.org/TR/n-quads/): `application/n-quads`
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* [RDF XML](https://www.w3.org/TR/rdf-syntax-grammar/): `application/rdf+xml`
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Example of loading a Turtle file into the named graph `<http://example.com/graph>` with the base IRI `http://example.com`:
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```python
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store.load('<http://example.com> <http://example.com> <> .', mime_type='text/turtle', base_iri="http://example.com", to_graph=NamedNode('http://example.com/graph'))
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```
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## How to contribute
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The Oxigraph bindings are written in Rust using [PyO3](https://github.com/PyO3/pyo3).
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They are build using [Maturin](https://github.com/PyO3/maturin).
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Maturin could be installed using the usual `pip install maturin`.
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To install development version of Oxigraph just run `maturin develop`.
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The Python bindings tests are written in Python.
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To run them use the usual `python -m unittest` in the `tests` directory.
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