Using RDF with Python

Nathan R. Yergler

Creative Commons

What This Talk Is

• Brief overview of RDF
• Very brief talk about why RDF matters
• Overview of your options as Python developers

What Is RDF?

• The short answer:

  An model for describing relationships and information, often encoded in XML.

• The long answer:

  RDF has an abstract syntax that reflects a simple graph-based data model, and formal semantics with a rigorously defined notion of entailment providing a basis for well founded deductions in RDF data.

RDF Statements

• Statements consisting of "triples"
• Subject, Predicate, Object
• Statements can be simple declarations:
  Nathan owns a dog.
• ...or containers, sequences, etc:
  The names of Nathan's dogs are Bosco and Madeline

Sample RDF Block

<rdf:RDF xmlns="http://web.resource.org/cc/"
    xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<Work rdf:about="">
   <license rdf:resource="http://creativecommons.org/licenses/by/2.0/" />
</Work>

<License rdf:about="http://creativecommons.org/licenses/by/2.0/">
   <permits rdf:resource="http://web.resource.org/cc/Reproduction" />
   <permits rdf:resource="http://web.resource.org/cc/Distribution" />
   <requires rdf:resource="http://web.resource.org/cc/Notice" />
   <requires rdf:resource="http://web.resource.org/cc/Attribution" />
   <permits rdf:resource="http://web.resource.org/cc/DerivativeWorks" />
</License>

</rdf:RDF>

Why is RDF Important?

• Objects get a fully qualified URI (http://web.resource.org/cc/License)
• Allows you to relate physically (and logically) disparate islands of information
• Allows the modeling of complex relationships
• Standardized model, so we can programmatically explore relationships

RDF In Use Today

• Creative Commons license declarations
• Edd Dumbhill's DOAP
• FOAF

RDF in Python

• Not a definitive list...
• rdflib
• pyrple
• Sparta

rdflib

• Largest, most diverse RDF handling library
• Create RDF by making assertions

>>> store = TripleStore()

>>> store.parse ( inputsource )

>>> rdf_subjects = store.subjects()

>>> store.predicates(subject="http://web.resource.org/cc/License")
 

pyrple

• Lightweight, "experimental" API
• In-memory triple store
• Very slick graph rule testing

>>> from pyrple import Triple

>>> from pyrple.namespaces import FOAF, VAR

>>> Triple(VAR.someone, FOAF.knows, VAR.person)
(?someone, , ?person)

pyrple

• Graph class represents a collection of triples
• query method returns list of triples which match the query parameter

sparta

• Wrapper around rdflib's TripleStore
• Maps RDF types to Python types
• Needs to bootstrap the TripleStore before using sparta methods

    from rdflib.TripleStore import TripleStore
    store = TripleStore()
    store.parse([URI])
    store.prefix_mapping([prefix], [URI])
    Thing = ThingFactory(store)

Real example... ccRdf

• Used for CC Applications that need to manipulate/read license data.
• Wraps rdflib with a dict-like interface

>>> rdf_string = """... rdf goes here ..."""
>>> ccr = ccRdf()
>>> ccr.parse(rdf_string)
>>> license = ccr.licenses()[0]
>>> licenses['requires']
['Attribution']

Conclusions

• RDF is a way of thinking...
• Not all problems have been solved yet
  • RDF in HTML, for example
• See the wiki for more information

Thanks!

• Questions?
• More information and updated samples available online:
  http://yergler.net/wiki/ynet/show/Python+and+RDF