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# standard imports
import itertools
import typing
# external imports
import rdflib
# bsfs imports
from bsfs.namespace import ns
from bsfs.utils import errors, URI, typename
# inner-module imports
from . import types
from . import schema
# exports
__all__: typing.Sequence[str] = (
'to_string',
'from_string',
)
## code ##
def from_string(schema_str: str) -> schema.Schema:
"""Load and return a Schema from a string."""
# parse string into rdf graph
graph = rdflib.Graph()
graph.parse(data=schema_str, format='turtle')
# helper functions
def _fetch_value(
subject: URI,
predicate: rdflib.URIRef,
value_factory: typing.Callable[[typing.Any], typing.Any],
) -> typing.Optional[typing.Any]:
"""Fetch the object of a given subject and predicate.
Raises a `errors.ConsistencyError` if multiple objects match.
"""
values = list(graph.objects(rdflib.URIRef(subject), predicate))
if len(values) == 0:
return None
if len(values) == 1:
return value_factory(values[0])
raise errors.ConsistencyError(
f'{subject} has multiple values for predicate {str(predicate)}, expected zero or one')
def _convert(value):
"""Convert the subject type from rdflib to a bsfs native type."""
if isinstance(value, rdflib.Literal):
return value.value
if isinstance(value, rdflib.URIRef):
return URI(value)
# value is neither a node nor a literal, but e.g. a blank node
raise errors.BackendError(f'expected Literal or URIRef, found {typename(value)}')
def _fetch_hierarchically(factory, curr):
"""Walk through a rdfs:subClassOf hierarchy, creating symbols along the way."""
# emit current node
yield curr
# walk through childs
for child in graph.subjects(rdflib.URIRef(ns.rdfs.subClassOf), rdflib.URIRef(curr.uri)):
# fetch annotations
annotations = {
URI(pred): _convert(value)
for pred, value # FIXME: preserve datatype of value?!
in graph.predicate_objects(child)
if URI(pred) != ns.rdfs.subClassOf
}
# convert child to URI
child = URI(child)
# check circular dependency
if child == curr.uri or child in {node.uri for node in curr.parents()}:
raise errors.ConsistencyError('circular dependency')
# recurse and emit (sub*)childs
yield from _fetch_hierarchically(factory, factory(child, curr, **annotations))
# fetch nodes
nodes = set(_fetch_hierarchically(types.Node, types.ROOT_NODE))
nodes_lut = {node.uri: node for node in nodes}
if len(nodes_lut) != len(nodes):
raise errors.ConsistencyError('inconsistent nodes')
# fetch literals
def _build_literal(uri, parent, **annotations):
"""Literal factory."""
# break out on root feature type
if uri == types.ROOT_FEATURE.uri:
return types.ROOT_FEATURE
# handle feature types
if isinstance(parent, types.Feature):
# clean annotations
annotations.pop(ns.bsfs.dimension, None)
annotations.pop(ns.bsfs.dtype, None)
annotations.pop(ns.bsfs.distance, None)
# get dimension
dimension = _fetch_value(uri, rdflib.URIRef(ns.bsfs.dimension), int)
# get dtype
dtype = _fetch_value(uri, rdflib.URIRef(ns.bsfs.dtype), URI)
# get distance
distance = _fetch_value(uri, rdflib.URIRef(ns.bsfs.distance), URI)
# return feature
return parent.child(URI(uri), dtype=dtype, dimension=dimension, distance=distance, **annotations)
# handle non-feature types
return parent.child(URI(uri), **annotations)
literals = set(_fetch_hierarchically(_build_literal, types.ROOT_LITERAL))
literals_lut = {lit.uri: lit for lit in literals}
if len(literals_lut) != len(literals):
raise errors.ConsistencyError('inconsistent literals')
# fetch predicates
def _build_predicate(uri, parent, **annotations):
"""Predicate factory."""
# clean annotations
annotations.pop(ns.rdfs.domain, None)
annotations.pop(ns.rdfs.range, None)
annotations.pop(ns.bsfs.unique, None)
# get domain
dom = _fetch_value(uri, rdflib.RDFS.domain, URI)
if dom is not None and dom not in nodes_lut:
raise errors.ConsistencyError(f'predicate {uri} has undefined domain {dom}')
if dom is not None:
dom = nodes_lut[dom]
# get range
rng = _fetch_value(uri, rdflib.RDFS.range, URI)
if rng is not None and rng not in nodes_lut and rng not in literals_lut:
raise errors.ConsistencyError(f'predicate {uri} has undefined range {rng}')
if rng is not None:
rng = nodes_lut.get(rng, literals_lut.get(rng))
# get unique
unique = _fetch_value(uri, rdflib.URIRef(ns.bsfs.unique), bool)
# build predicate
return parent.child(URI(uri), domain=dom, range=rng, unique=unique, **annotations)
predicates = _fetch_hierarchically(_build_predicate, types.ROOT_PREDICATE)
return schema.Schema(predicates, nodes, literals)
def to_string(schema_inst: schema.Schema, fmt: str = 'turtle') -> str:
"""Serialize a `bsfs.schema.Schema` to a string.
See `rdflib.Graph.serialize` for viable formats (default: turtle).
"""
# type of emitted triples.
T_TRIPLE = typing.Iterator[typing.Tuple[rdflib.URIRef, rdflib.URIRef, rdflib.term.Identifier]]
def _type(tpe: types._Type) -> T_TRIPLE :
"""Emit _Type properties (parent, annotations)."""
# emit parent
if tpe.parent is not None:
yield (
rdflib.URIRef(tpe.uri),
rdflib.URIRef(ns.rdfs.subClassOf),
rdflib.URIRef(tpe.parent.uri),
)
# emit annotations
for prop, value in tpe.annotations.items():
yield (
rdflib.URIRef(tpe.uri),
rdflib.URIRef(prop),
rdflib.Literal(value), # FIXME: datatype?!
)
def _predicate(pred: types.Predicate) -> T_TRIPLE:
"""Emit Predicate properties (domain, range, unique)."""
# no need to emit anything for the root predicate
if pred == types.ROOT_PREDICATE:
return
# emit domain
if pred.domain != getattr(pred.parent, 'domain', None):
yield (
rdflib.URIRef(pred.uri),
rdflib.URIRef(ns.rdfs.domain),
rdflib.URIRef(pred.domain.uri),
)
# emit range
if pred.range != getattr(pred.parent, 'range', None):
yield (
rdflib.URIRef(pred.uri),
rdflib.URIRef(ns.rdfs.range),
rdflib.URIRef(pred.range.uri),
)
# emit cardinality
if pred.unique != getattr(pred.parent, 'unique', None):
yield (
rdflib.URIRef(pred.uri),
rdflib.URIRef(ns.bsfs.unique),
rdflib.Literal(pred.unique, datatype=rdflib.XSD.boolean),
)
def _feature(feat: types.Feature) -> T_TRIPLE:
"""Emit Feature properties (dimension, dtype, distance)."""
# emit size
if feat.dimension != getattr(feat.parent, 'dimension', None):
yield (
rdflib.URIRef(feat.uri),
rdflib.URIRef(ns.bsfs.dimension),
rdflib.Literal(feat.dimension, datatype=rdflib.XSD.integer),
)
# emit dtype
if feat.dtype != getattr(feat.parent, 'dtype', None):
yield (
rdflib.URIRef(feat.uri),
rdflib.URIRef(ns.bsfs.dtype),
rdflib.URIRef(feat.dtype),
)
# emit distance
if feat.distance != getattr(feat.parent, 'distance', None):
yield (
rdflib.URIRef(feat.uri),
rdflib.URIRef(ns.bsfs.distance),
rdflib.URIRef(feat.distance),
)
def _parse(node: types._Type) -> T_TRIPLE:
"""Emit all properties of a type."""
# check arg
if not isinstance(node, types._Type): # pylint: disable=protected-access
raise TypeError(node)
# emit _Type essentials
yield from _type(node)
# emit properties of derived types
if isinstance(node, types.Predicate):
yield from _predicate(node)
if isinstance(node, types.Feature):
yield from _feature(node)
# create graph
graph = rdflib.Graph()
# add triples to graph
nodes = itertools.chain(
schema_inst.nodes(),
schema_inst.literals(),
schema_inst.predicates())
for node in nodes:
for triple in _parse(node):
graph.add(triple)
# add known namespaces for readability
# FIXME: more generically?
graph.bind('bse', rdflib.URIRef(ns.bse['']))
graph.bind('bsfs', rdflib.URIRef(ns.bsfs['']))
graph.bind('bsm', rdflib.URIRef(ns.bsm['']))
graph.bind('rdf', rdflib.URIRef(ns.rdf['']))
graph.bind('rdfs', rdflib.URIRef(ns.rdfs['']))
graph.bind('schema', rdflib.URIRef(ns.schema['']))
graph.bind('xsd', rdflib.URIRef(ns.xsd['']))
# serialize to turtle
return graph.serialize(format=fmt)
## EOF ##
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