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"""
An example illustrating how to use the
[`Graph.transitive_subjects`][rdflib.graph.Graph.transitive_subjects] and
[`Graph.transitive_objects`][rdflib.graph.Graph.transitive_objects] graph methods
## Formal definition
The [`Graph.transitive_objects`][rdflib.graph.Graph.transitive_objects] method finds all
nodes such that there is a path from subject to one of those nodes
using only the predicate property in the triples. The
[`Graph.transitive_subjects`][rdflib.graph.Graph.transitive_subjects] method is similar; it
finds all nodes such that there is a path from the node to the object
using only the predicate property.
## Informal description, with an example
In brief, [`Graph.transitive_objects`][rdflib.graph.Graph.transitive_objects] walks forward
in a graph using a particular property, and
[`Graph.transitive_subjects`][rdflib.graph.Graph.transitive_subjects] walks backward. A good
example uses a property `ex:parent`, the semantics of which are
biological parentage. The
[`Graph.transitive_objects`][rdflib.graph.Graph.transitive_objects] method would get all
the ancestors of a particular person (all nodes such that there is a
parent path between the person and the object). The
[`Graph.transitive_subjects`][rdflib.graph.Graph.transitive_subjects] method would get all
the descendants of a particular person (all nodes such that there is a
parent path between the node and the person). So, say that your URI is
`ex:person`.
This example would get all of your (known) ancestors, and then get all
the (known) descendants of your maternal grandmother.
!!! warning "Important note on arguments"
The [`Graph.transitive_objects`][rdflib.graph.Graph.transitive_objects] method has the start node
as the *first* argument, but the [`Graph.transitive_subjects`][rdflib.graph.Graph.transitive_subjects]
method has the start node as the *second* argument.
## User-defined transitive closures
The method [`Graph.transitiveClosure`][rdflib.graph.Graph.transitiveClosure] returns
transtive closures of user-defined functions.
"""
if __name__ == "__main__":
from rdflib import ConjunctiveGraph, URIRef
person = URIRef("ex:person")
dad = URIRef("ex:d")
mom = URIRef("ex:m")
momOfDad = URIRef("ex:gm0") # noqa: N816
momOfMom = URIRef("ex:gm1") # noqa: N816
dadOfDad = URIRef("ex:gf0") # noqa: N816
dadOfMom = URIRef("ex:gf1") # noqa: N816
parent = URIRef("ex:parent")
g = ConjunctiveGraph()
g.add((person, parent, dad))
g.add((person, parent, mom))
g.add((dad, parent, momOfDad))
g.add((dad, parent, dadOfDad))
g.add((mom, parent, momOfMom))
g.add((mom, parent, dadOfMom))
print("Parents, forward from `ex:person`:")
for i in g.transitive_objects(person, parent):
print(i)
print("Parents, *backward* from `ex:gm1`:")
for i in g.transitive_subjects(parent, momOfMom):
print(i)
|
