Hi, I hope this is the correct list for contributions. We use rdflib to parse RDF files (RDF files describing computer networks), and are pleased with the power of RDFlib. However, documentation is, well, nearly non-existant (the API documentation and two examples).
An upgrade to 2.4.0 actually gave a few disgruntled faces, since it broke our code (in particular, the helpful hints still available at http://dev.w3.org/cvsweb/~checkout~/2004/PythonLib-IH/Doc/sparqlDesc.html don't work anymore for two incompatible changes (sparqlGrph.query() takes different parameters, and the "shortcut" rdflib.sparql.SPARQLGraph is gone). So I tried to create an example which highlight tree different ways to find triplets in an RDF file: 1. Simple lookup in a list of triplets, 2. SPARQL query, created with rdflib.sparql.* objects, and 3. SPARQL query, created with bison. Also, I build in version checks, to take into account that: - bison was only added in RDFlib 2.3.3 and - the function calls for method 2 are changes in RDFlib 2.4.0. The example script is attached. I put it in the public domain; feel free to change, include, modify, curse, attribute or stick your own copyright to it. In case the list does not accept attachements, I put it also on-line at http://www.science.uva.nl/research/air/wiki/RDFlib Regards, Freek Dijkstra Universiteit van Amsterdam
#!/usr/bin/env python # -*- coding: utf-8 -*- """Demo script to show the different ways to read information from an RDF file using rdflib, as found at http://rdflib.net/. The tree main methods are: 1. Simple lookup in a list of triplets (SimpleLookup), 2. SPARQL query, created with rdflib.sparql.* objects (CustomSparql), 3. SPARQL query, created with bison (BisonSparql). The main function reads a file, xfn-example.rdf, and displays all resource pairs with a symmetrical "xfn:met" relation (e.g. A met B and B met A) Uses the rdfs:label of the resources to display the name. This demo file has been tested with the following versions of RDFlib: rdflib 2.0.6 -- unsupported (since it has no "Graph" modules) rdflib 2.1.3 -- methods 1, and 2 work fine rdflib 2.1.4 -- methods 1, and 2 work fine rdflib 2.2.3 -- methods 1, and 2 work fine rdflib 2.3.0 -- methods 1, and 2 work fine rdflib 2.3.1 -- methods 1, and 2 work fine rdflib 2.3.2 -- methods 1, and 2 work fine rdflib 2.3.3 -- methods 1, 2, and 3 work fine rdflib 2.4.0 -- methods 1, 2, and 3 work fine (but function call for method 2 was changed) """ __copyright__ = "rdflibdemo written by Freek Dijkstra, Universiteit van Amsterdam, april 2007, contributed to the public domain (feel free to attribute me, but it's not needed)." import os import sys import distutils.version # semi-standard modules try: import rdflib except ImportError: raise ImportError("Module rdflib is not available. It can be downloaded from http://rdflib.net/\n";) if distutils.version.StrictVersion(rdflib.__version__) < "2.0.9": raise ImportError("The installed version of rdflib, %s, is too old. 2.1 or higher is required" % rdflib.__version__) from rdflib.Graph import Graph from rdflib.sparql.sparqlGraph import SPARQLGraph from rdflib.sparql.graphPattern import GraphPattern if distutils.version.StrictVersion(rdflib.__version__) > "2.3.2": from rdflib.sparql.bison import Parse # available in 2.3.3 and up if distutils.version.StrictVersion(rdflib.__version__) > "2.3.9": from rdflib.sparql import Query # available in 2.4.0 and up def SimpleLookup(graph): """ Extracts information form a rdflib Graph object using a simple list lookup. E.g.: result = list(graph.subject_objects(self.xfn["met"])): """ assert(isinstance(graph, Graph)) xfn = rdflib.Namespace("http://gmpg.org/xfn/1#";) rdf = rdflib.Namespace("http://www.w3.org/1999/02/22-rdf-syntax-ns#";) rdfs = rdflib.Namespace("http://www.w3.org/2000/01/rdf-schema#";) meetings = [] # Get a list of (subject, object) tuples in the graph with the xfn:met predicate relations = list(graph.subject_objects(xfn["met"])) for (person, peer) in relations: if not (peer, person) in relations: # person says he/she has met peer, but peer doesn't say he/she has met person. Skip. continue # since we're processing (person, peer), we can skip (peer, person) later relations.remove((peer, person)) personname = list(graph.objects(person, rdfs["label"])) if len(personname) == 0: continue # skip persons with no name peername = list(graph.objects(peer, rdfs["label"])) if len(peername) == 0: continue # skip peers with no name personname = list(graph.objects(person, rdfs["label"])) # Add the name of the person and peer to list of people who've met. meetings.append((personname[0], peername[0])) # Print the results print "Simple Lookup (%d meetings found)" % len(meetings) print 40*"-" for (person, peer) in meetings: print "%s and %s have met" % (person, peer) print def CustomSparql(graph): """ Extracts information form a rdflib Graph object using a SPARQL query, put together using GraphPattern objects. E.g.: select = ("?ifA","?ifB") where = GraphPattern([("?ifA", xfn["met"], "?ifB")]) result = graph.query(select,where) See http://dev.w3.org/cvsweb/~checkout~/2004/PythonLib-IH/Doc/sparqlDesc.html for more information. """ assert(isinstance(graph, Graph)) xfn = rdflib.Namespace("http://gmpg.org/xfn/1#";) rdf = rdflib.Namespace("http://www.w3.org/1999/02/22-rdf-syntax-ns#";) rdfs = rdflib.Namespace("http://www.w3.org/2000/01/rdf-schema#";) select = ("?personname","?peername") where = GraphPattern([ ("?person", xfn["met"], "?peer"), ("?peer", xfn["met"], "?person"), ("?person", rdfs["label"], "?personname"), ("?peer", rdfs["label"], "?peername"), ]) # Create a SPARQLGraph wrapper object out of the normal Graph sparqlGrph = SPARQLGraph(graph) # Make the query if distutils.version.StrictVersion(rdflib.__version__) <= "2.3.9": relations = sparqlGrph.query(select, where) else: # graph.query() function was changed in RDFlib 2.4.0 bindings = { u"xfn": xfn, u"rdf": rdf, u"rdfs": rdfs } relations = Query.query(sparqlGrph, select, where, initialBindings=bindings) for (person, peer) in relations: # since we're processing (person, peer), we can skip (peer, person) later relations.remove((peer, person)) # Print the results print "Manual formatted SPARQL query (%d meetings found)" % len(relations) print 40*"-" for (person, peer) in relations: print "%s and %s have met" % (person, peer) print def BisonSparql(graph): """ Extracts information form a rdflib Graph object using a SPARQL query, parsed by the bison parser in RDFlib. graphpattern = Parse('SELECT ?ifA ?ifB WHERE { ?ifA xfn:met ?ifB . ?ifB xfn:met ?ifA }') result = graph.query(graphpattern, initNs=bindings) """ assert(isinstance(graph, Graph)) if distutils.version.StrictVersion(rdflib.__version__) <= "2.3.2": print "Skipping Bison SPARQL query (requires RDFlib 2.3.3 or higher; version %s detected)" % (rdflib.__version__) print return xfn = rdflib.Namespace("http://gmpg.org/xfn/1#";) rdf = rdflib.Namespace("http://www.w3.org/1999/02/22-rdf-syntax-ns#";) rdfs = rdflib.Namespace("http://www.w3.org/2000/01/rdf-schema#";) bindings = { u"xfn": xfn, u"rdf": rdf, u"rdfs": rdfs } query = Parse('SELECT ?personname ?peername WHERE \ { ?person xfn:met ?peer . ?peer xfn:met ?person . \ ?person rdfs:label ?personname . ?peer rdfs:label ?peername }') # Make the query, and serialize the result as python objects (as opposed to for example XML) relations = graph.query(query, initNs=bindings).serialize('python') for (person, peer) in relations: # since we're processing (person, peer), we can skip (peer, person) later relations.remove((peer, person)) # Print the results print "Bison SPARQL query (%d meetings found)" % len(relations) print 40*"-" for (person, peer) in relations: print "%s and %s have met" % (person, peer) print def ReadFile(filename="xfn-example.rdf"): """Read a RDF and returns the objects in a rdflib Graph object""" graph = Graph() print "Read RDF data from %s" % filename print graph.parse(filename) return graph if __name__=="__main__": print "RDFlib version %s detected" % rdflib.__version__ print graph = ReadFile() SimpleLookup(graph) CustomSparql(graph) BisonSparql(graph)
xfn-example.rdf
Description: application/rdf
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