Re: [rdflib-dev] Example code

[Calvin Hendryx-Parker]

Maybe we should throw up a wiki for user documentation? It would be of real value to have this in a central place. In addition it would be nice to have the epydoc generated docs on the site too. I generated them, but they are ancient now.

My $0.02

Cal

On Apr 23, 2007, at 7:44 PM, Freek Dijkstra wrote:

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()

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.


to it.


http://www.science.uva.nl/research/air/wiki/RDFlib

Regards,
Freek Dijkstra
Universiteit van Amsterdam
#!/usr/bin/env python
# -*- coding: utf-8 -*-

takes different parameters, and the "shortcut" rdflib.sparql.SPARQLGraph 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 In case the list does not accept attachements, I put it also on- line at """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).


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

"""



import os
import sys
import distutils.version
# semi-standard modules
try:
    import rdflib
except ImportError:

The main function reads a file, xfn-example.rdf, and displays all resource 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)." 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":

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":

if distutils.version.StrictVersion(rdflib.__version__) > "2.3.9":





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#";)

raise ImportError("The installed version of rdflib, %s, is too old. 2.1 or higher is required" % rdflib.__version__) from rdflib.sparql.bison import Parse # available in 2.3.3 and up from rdflib.sparql import Query # available in 2.4.0 and up 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 = []

    relations = list(graph.subject_objects(xfn["met"]))
    for (person, peer) in relations:
        if not (peer, person) in relations:

            continue

        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"]))

        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

    select = ("?ifA","?ifB")
    where = GraphPattern([("?ifA", xfn["met"], "?ifB")])
    result = graph.query(select,where)

# Get a list of (subject, object) tuples in the graph with the xfn:met predicate # person says he/she has met peer, but peer doesn't say he/she has met person. Skip. # since we're processing (person, peer), we can skip (peer, person) later # Add the name of the person and peer to list of people who've met. using a SPARQL query, put together using GraphPattern objects. E.g.: 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 }


    for (person, peer) in relations:

        relations.remove((peer, person))

    # Print the results

    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.

    result = graph.query(graphpattern, initNs=bindings)
    """
    assert(isinstance(graph, Graph))
    if distutils.version.StrictVersion(rdflib.__version__) <= "2.3.2":

        print
        return
    xfn  = rdflib.Namespace("http://gmpg.org/xfn/1#";)

relations = Query.query(sparqlGrph, select, where, initialBindings=bindings) # since we're processing (person, peer), we can skip (peer, person) later print "Manual formatted SPARQL query (%d meetings found)" % len (relations) graphpattern = Parse('SELECT ?ifA ?ifB WHERE { ?ifA xfn:met ? ifB . ?ifB xfn:met ?ifA }') print "Skipping Bison SPARQL query (requires RDFlib 2.3.3 or higher; version %s detected)" % (rdflib.__version__) 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 . \

    for (person, peer) in relations:

        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>
_______________________________________________
Dev mailing list
Dev@rdflib.net
http://rdflib.net/mailman/listinfo/dev

?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') # since we're processing (person, peer), we can skip (peer, person) later

--
S i x  F e e t  U p , I n c .  |  "Nowhere to go but open source"
Silicon Valley: +1 (650) 401-8579 x602
Midwest: +1 (317) 861-5948 x602
Toll-Free: 1-866-SIX-FEET
mailto:[EMAIL PROTECTED]
http://www.sixfeetup.com  |  Zope/Plone Custom Development

PGP.sig
Description: This is a digitally signed message part

_______________________________________________
Dev mailing list
Dev@rdflib.net
http://rdflib.net/mailman/listinfo/dev