Transitive Traversal¶
How to use the transitive_objects
and transitive_subjects
graph methods.
Formal definition¶
The 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 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, transitive_objects
walks forward8 in a graph using a particular
property and ``transitive_subjects`` walks *backward.
A good example uses a property ex:parent
, the semantics of which are
biological parentage.
The 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 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
. The following code would get all of
your (known) ancestors, and then get all the (known) descendants of your
maternal grandmother:
from rdflib import ConjunctiveGraph, URIRef
person = URIRef('ex:person')
dad = URIRef('ex:d')
mom = URIRef('ex:m')
momOfDad = URIRef('ex:gm0')
momOfMom = URIRef('ex:gm1')
dadOfDad = URIRef('ex:gf0')
dadOfMom = URIRef('ex:gf1')
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)
Warning
The transitive_objects
method has the start
node as the first argument, but the transitive_subjects
method has the start
node as the second argument.