Source code for examples.custom_eval

This example shows how a custom evaluation function can be added to
handle certain SPARQL Algebra elements.

A custom function is added that adds ``rdfs:subClassOf`` "inference" when
asking for ``rdf:type`` triples.

Here the custom eval function is added manually, normally you would use
setuptools and entry_points to do it:
i.e. in your

    entry_points = {
        'rdf.plugins.sparqleval': [
            'myfunc =     mypackage:MyFunction',

import rdflib

from rdflib.plugins.sparql.evaluate import evalBGP
from rdflib.namespace import FOAF

inferredSubClass = rdflib.RDFS.subClassOf * "*"  # any number of rdfs.subClassOf

[docs]def customEval(ctx, part): """ Rewrite triple patterns to get super-classes """ if == "BGP": # rewrite triples triples = [] for t in part.triples: if t[1] == rdflib.RDF.type: bnode = rdflib.BNode() triples.append((t[0], t[1], bnode)) triples.append((bnode, inferredSubClass, t[2])) else: triples.append(t) # delegate to normal evalBGP return evalBGP(ctx, triples) raise NotImplementedError()
if __name__ == "__main__": # add function directly, normally we would use setuptools and entry_points rdflib.plugins.sparql.CUSTOM_EVALS["exampleEval"] = customEval g = rdflib.Graph() g.load("foaf.n3") # Add the subClassStmt so that we can query for it! g.add((FOAF.Person, rdflib.RDFS.subClassOf, FOAF.Agent)) # Find all FOAF Agents for x in g.query("PREFIX foaf: <%s> SELECT * WHERE { ?s a foaf:Agent . }" % FOAF): print(x)