Bill Kearney

Some RDF examples

Take this snippet of RDF and paste it into the RDF validator. Note you'll probably want to make sure you pull down the "Graph Only" option.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:eg="http://example.org/foovocab#"
  xmlns:foaf="http://xmlns.com/foaf/0.1/">
	<foaf:Person rdf:nodeID="p1">
	    <foaf:name>Alice</foaf:name>
	    <foaf:knows>
		<foaf:Person rdf:nodeID="p2">
		    <foaf:name>Bob</foaf:name>
		    <eg:secretlyStalking rdf:nodeID="p1"/>
		</foaf:Person>
	    </foaf:knows>
	    <eg:acquaintance rdf:nodeID="p2"/>
	    <eg:archNemesis rdf:nodeID="p2"/>
	</foaf:Person>
</rdf:RDF>

Now take this snippet, open a new window to the RDF validator and check it.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:eg="http://example.org/foovocab#"
  xmlns:foaf="http://xmlns.com/foaf/0.1/">
	<foaf:Person rdf:nodeID="p1">
	    <foaf:name>Alice</foaf:name>
	    <foaf:knows rdf:nodeID="p2"/>
	    <eg:acquaintance rdf:nodeID="p2"/>
	    <eg:archNemesis rdf:nodeID="p2"/>
	</foaf:Person>
	<foaf:Person rdf:nodeID="p2">
	    <foaf:name>Bob</foaf:name>
	    <eg:secretlyStalking rdf:nodeID="p1"/>
	</foaf:Person>
</rdf:RDF>

Notice the pictures? They're THE SAME. How is this possible? The second one doesn't use the same ordering of the data as the first. And yet the graphs are exactly alike. This is important. Using RDF allows you to provide data that's got meaning independent of the restrictions imposed by the hierachical nature of XML.

It get's more interesting when you start to have a LOT of people with varying degrees of interconnectedness. Cut-and-paste this snippet into the validator:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:eg="http://example.org/foovocab#"
  xmlns:foaf="http://xmlns.com/foaf/0.1/">
	<foaf:Person rdf:nodeID="alice">
	    <foaf:name>Alice</foaf:name>
	    <foaf:knows rdf:nodeID="bob"/>
	    <foaf:knows rdf:nodeID="ted"/>
	    <eg:acquaintance rdf:nodeID="bob"/>
	    <eg:acquaintance rdf:nodeID="ted"/>
	    <eg:archNemesis rdf:nodeID="bob"/>
	    <eg:archNemesis rdf:nodeID="ted"/>
	</foaf:Person>
	<foaf:Person rdf:nodeID="bob">
	    <foaf:knows rdf:nodeID="alice"/>
	    <foaf:knows rdf:nodeID="ted"/>
	    <foaf:name>Bob</foaf:name>
	    <eg:secretlyStalking rdf:nodeID="alice"/>
	    <eg:acquaintance rdf:nodeID="alice"/>
	    <eg:archNemesis rdf:nodeID="ted"/>
	</foaf:Person>
	<foaf:Person rdf:nodeID="carol">
	    <foaf:name>Carol</foaf:name>
	    <foaf:knows rdf:nodeID="alice"/>
	    <foaf:knows rdf:nodeID="ted"/>
	    <eg:secretlyStalking rdf:nodeID="bob"/>
	    <eg:acquaintance rdf:nodeID="alice"/>
	    <eg:acquaintance rdf:nodeID="ted"/>
	</foaf:Person>
	<foaf:Person rdf:nodeID="ted">
	    <foaf:name>Ted</foaf:name>
	    <eg:acquaintance rdf:nodeID="carol"/>
	    <eg:acquaintance rdf:nodeID="alice"/>
	    <eg:archNemesis rdf:nodeID="bob"/>
	</foaf:Person>
</rdf:RDF>

Here you have a graph showing very complex set of relationships. Yet the RDF/XML file is very compact and not verbose at all. The amazing thing about RDF is I could then query the triples for just the http://xmlns.com/foaf/0.1/knows URI and immediately extract who knows who. No DOM or SAX navigating needed at all.

So when you hear some developers carping about how the supposed verboseness of RDF, think about what it would take to fix the half-baked alternatives they're espousing. Especially when things start to get very interconnected. Using plain old XML would certainly be possible but why? There's already a growing body of tools that support using RDF.

There's more to the story folks, don't believe the crap the simpletons keep spouting. It's just not true.

# cribbed from
#  http://rdflib.net/stable/example.py

from rdflib.TripleStore import TripleStore

from rdflib.constants import TYPE

from rdflib.Namespace import Namespace

from rdflib.Literal import Literal

FOAF = Namespace("http://xmlns.com/foaf/0.1/")

EX = Namespace("http://example.org/foovocab#")

def main():

    s = TripleStore()

    s.load(",ex2.rdf")

    # find a guy named bob...

    for who in s.subjects(FOAF["name"], Literal("Bob")):

        bob = who

    

    # who is secretlyStalking bob?

    for who in s.subjects(EX["secretlyStalking"], bob):

        for n in s.objects(who, FOAF["name"]):

            print n, "is secretlyStalking Bob!"

if __name__ == '__main__':

    main()