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Diffstat (limited to 'bsfs/triple_store/sparql/sparql.py')
| -rw-r--r-- | bsfs/triple_store/sparql/sparql.py | 297 |
1 files changed, 297 insertions, 0 deletions
diff --git a/bsfs/triple_store/sparql/sparql.py b/bsfs/triple_store/sparql/sparql.py new file mode 100644 index 0000000..c3cbff6 --- /dev/null +++ b/bsfs/triple_store/sparql/sparql.py @@ -0,0 +1,297 @@ +""" + +Part of the BlackStar filesystem (bsfs) module. +A copy of the license is provided with the project. +Author: Matthias Baumgartner, 2022 +""" +# imports +import itertools +import typing +import rdflib + +# bsfs imports +from bsfs import schema as bsc +from bsfs.query import ast +from bsfs.utils import errors, URI + +# inner-module imports +from . import parse_filter +from .. import base + + +# exports +__all__: typing.Sequence[str] = ( + 'SparqlStore', + ) + + +## code ## + +class _Transaction(): + """Lightweight rdflib transactions for in-memory databases.""" + + # graph instance. + _graph: rdflib.Graph + + # current log of added triples. + _added: typing.List[typing.Any] + + # current log of removed triples. + _removed: typing.List[typing.Any] + + def __init__(self, graph: rdflib.Graph): + self._graph = graph + # initialize internal structures + self.commit() + + def commit(self): + """Commit temporary changes.""" + self._added = [] + self._removed = [] + + def rollback(self): + """Undo changes since the last commit.""" + for triple in self._added: + self._graph.remove(triple) + for triple in self._removed: + self._graph.add(triple) + + def add(self, triple: typing.Any): + """Add a triple to the graph.""" + if triple not in self._graph: + self._added.append(triple) + self._graph.add(triple) + + def remove(self, triple: typing.Any): + """Remove a triple from the graph.""" + if triple in self._graph: + self._removed.append(triple) + self._graph.remove(triple) + + +class SparqlStore(base.TripleStoreBase): + """Sparql-based triple store. + + The sparql triple store uses a third-party backend + (currently rdflib) to store triples and manages them via + the Sparql query language. + + """ + + # The rdflib graph. + _graph: rdflib.Graph + + # Current transaction. + _transaction: _Transaction + + # The local schema. + _schema: bsc.Schema + + # Filter parser + _filter_parser: parse_filter.Filter + + def __init__(self): + super().__init__(None) + self._graph = rdflib.Graph() + self._transaction = _Transaction(self._graph) + self._schema = bsc.Schema.Empty() + self._filter_parser = parse_filter.Filter(self._schema) + + # NOTE: mypy and pylint complain about the **kwargs not being listed (contrasting super) + # However, not having it here is clearer since it's explicit that there are no arguments. + @classmethod + def Open(cls) -> 'SparqlStore': # type: ignore [override] # pylint: disable=arguments-differ + return cls() + + def commit(self): + self._transaction.commit() + + def rollback(self): + self._transaction.rollback() + + @property + def schema(self) -> bsc.Schema: + return self._schema + + @schema.setter + def schema(self, schema: bsc.Schema): + # check args: Schema instanace + if not isinstance(schema, bsc.Schema): + raise TypeError(schema) + # check compatibility: No contradicting definitions + if not self.schema.consistent_with(schema): + raise errors.ConsistencyError(f'{schema} is inconsistent with {self.schema}') + + # commit the current transaction + self.commit() + + # adjust instances: + # nothing to do for added classes + # delete instances of removed classes + + # get deleted classes + sub = self.schema - schema + + for pred in sub.predicates: + # remove predicate instances + for src, trg in self._graph.subject_objects(rdflib.URIRef(pred.uri)): + self._transaction.remove((src, rdflib.URIRef(pred.uri), trg)) + # remove predicate definition + if pred.parent is not None: + self._transaction.remove(( + rdflib.URIRef(pred.uri), + rdflib.RDFS.subClassOf, + rdflib.URIRef(pred.parent.uri), + )) + + # remove node instances + for node in sub.nodes: + # iterate through node instances + for inst in self._graph.subjects(rdflib.RDF.type, rdflib.URIRef(node.uri)): + # remove triples where the instance is in the object position + for src, pred in self._graph.subject_predicates(inst): + self._transaction.remove((src, pred, inst)) + # remove triples where the instance is in the subject position + for pred, trg in self._graph.predicate_objects(inst): + self._transaction.remove((inst, pred, trg)) + # remove instance + self._transaction.remove((inst, rdflib.RDF.type, rdflib.URIRef(node.uri))) + # remove node definition + if node.parent is not None: + self._transaction.remove(( + rdflib.URIRef(node.uri), + rdflib.RDFS.subClassOf, + rdflib.URIRef(node.parent.uri), + )) + + for lit in sub.literals: + # remove literal definition + if lit.parent is not None: + self._transaction.remove(( + rdflib.URIRef(lit.uri), + rdflib.RDFS.subClassOf, + rdflib.URIRef(lit.parent.uri), + )) + + # add predicate, node, and literal hierarchies to the graph + for itm in itertools.chain(schema.predicates(), schema.nodes(), schema.literals()): + if itm.parent is not None: + self._transaction.add((rdflib.URIRef(itm.uri), rdflib.RDFS.subClassOf, rdflib.URIRef(itm.parent.uri))) + + # commit instance changes + self.commit() + + # migrate schema + self._schema = schema + self._filter_parser.schema = schema + + def get( + self, + node_type: bsc.Node, + query: typing.Optional[ast.filter.FilterExpression] = None, + ) -> typing.Iterator[URI]: + if node_type not in self.schema.nodes(): + raise errors.ConsistencyError(f'{node_type} is not defined in the schema') + if not isinstance(query, ast.filter.FilterExpression): + raise TypeError(query) + for guid, in self._graph.query(self._filter_parser(node_type, query)): + yield URI(guid) + + def _has_type(self, subject: URI, node_type: bsc.Node) -> bool: + """Return True if *subject* is a node of class *node_type* or a subclass thereof.""" + if node_type not in self.schema.nodes(): + raise errors.ConsistencyError(f'{node_type} is not defined in the schema') + + subject_types = list(self._graph.objects(rdflib.URIRef(subject), rdflib.RDF.type)) + if len(subject_types) == 0: + return False + if len(subject_types) == 1: + node = self.schema.node(URI(subject_types[0])) # type: ignore [arg-type] # URI is a subtype of str + if node == node_type: + return True + if node_type in node.parents(): + return True + return False + raise errors.UnreachableError() + + def exists( + self, + node_type: bsc.Node, + guids: typing.Iterable[URI], + ) -> typing.Iterable[URI]: + return (subj for subj in guids if self._has_type(subj, node_type)) + + def create( + self, + node_type: bsc.Node, + guids: typing.Iterable[URI], + ): + # check node_type + if node_type not in self.schema.nodes(): + raise errors.ConsistencyError(f'{node_type} is not defined in the schema') + # check and create guids + for guid in guids: + subject = rdflib.URIRef(guid) + # check node existence + if (subject, rdflib.RDF.type, None) in self._graph: + # FIXME: node exists and may have a different type! ignore? raise? report? + continue + # add node + self._transaction.add((subject, rdflib.RDF.type, rdflib.URIRef(node_type.uri))) + + def set( + self, + node_type: bsc.Node, + guids: typing.Iterable[URI], + predicate: bsc.Predicate, + values: typing.Iterable[typing.Any], + ): + # check node_type + if node_type not in self.schema.nodes(): + raise errors.ConsistencyError(f'{node_type} is not defined in the schema') + # check predicate + if predicate not in self.schema.predicates(): + raise errors.ConsistencyError(f'{predicate} is not defined in the schema') + if not node_type <= predicate.domain: + raise errors.ConsistencyError(f'{node_type} must be a subclass of {predicate.domain}') + # NOTE: predicate.range is in the schema since predicate is in the schema. + # materialize values + values = set(values) + # check values + if len(values) == 0: + return + if predicate.unique and len(values) != 1: + raise ValueError(values) + if isinstance(predicate.range, bsc.Node): + values = set(values) # materialize to safeguard against iterators passed as argument + inconsistent = {val for val in values if not self._has_type(val, predicate.range)} + # catches nodes that don't exist and nodes that have an inconsistent type + if len(inconsistent) > 0: + raise errors.InstanceError(inconsistent) + # check guids + # FIXME: Fail or skip inexistent nodes? + guids = set(guids) + inconsistent = {guid for guid in guids if not self._has_type(guid, node_type)} + if len(inconsistent) > 0: + raise errors.InstanceError(inconsistent) + + # add triples + pred = rdflib.URIRef(predicate.uri) + for guid, value in itertools.product(guids, values): + guid = rdflib.URIRef(guid) + # convert value + if isinstance(predicate.range, bsc.Literal): + value = rdflib.Literal(value, datatype=rdflib.URIRef(predicate.range.uri)) + elif isinstance(predicate.range, bsc.Node): + value = rdflib.URIRef(value) + else: + raise errors.UnreachableError() + # clear triples for unique predicates + if predicate.unique: + for obj in self._graph.objects(guid, pred): + if obj != value: + self._transaction.remove((guid, pred, obj)) + # add triple + self._transaction.add((guid, pred, value)) + +## EOF ## |