While exploring the Subject Headings Linked Data Space (LCSH) recently unveiled by the Library of Congress, I noticed that the URI for the subject heading: World Wide Web, exposes an "owl:sameAs" link to resource URI: "info:lc/authorities/sh95000541" -- in fact, a URI.URN that isn't HTTP protocol scheme based.
The observations above triggered a discussion thread on Twitter that involved: @edsu, @iand, and moi. Naturally, it morphed into a live demonstration of: human vs machine, interpretation of claims expressed in the RDF graph.
What makes this whole thing interesting?
It showcases (in Man vs Machine style) the issue of unambiguously discerning the meaning of the owl:sameAs claim expressed in the LCSH Linked Data Space.
Perspectives & Potential Confusion
From the Linked Data perspective, it may spook a few people to see owl:sameAs values such as: "info:lc/authorities/sh95000541", that cannot be de-referenced using HTTP.
It may confuse a few people or user agents that see URI de-referencing as not necessarily HTTP specific, thereby attempting to de-reference the URI.URN on the assumption that it's associated with a "handle system", for instance.
It may even confuse RDFizer / RDFization middleware that use owl:sameAs as a data provider attribution mechanism via hint/nudge URI values derived from original content / data URI.URLs that de-reference to nothing e.g., an original resource URI.URL plus "#this" which produces URI.URN-URL -- think of this pattern as "owl:shameAs" in a sense :-)
Unambiguously Discerning Meaning
Simply bring OWL reasoning (inference rules and reasoners) into the mix, thereby negating human dialogue about interpretation which ultimately unveils a mesh of orthogonal view points. Remember, OWL is all about infrastructure that ultimately enables you to express yourself clearly i.e., say what you mean, and mean what you say.
Path to Clarity (using Virtuoso, its in-built Sponger Middleware, and Inference Engine):
- GET the data into the Virtuoso Quad store -- what the sponger does via its URIBurner Service (while following designated predicates such as owl:sameAs in case they point to other mesh-able data sources)
- Query the data in Quad Store with "owl:sameAs" inference rules enabled
- Repeat the last step with the inference rules excluded.
Actual SPARQL Queries:
- SPARQL Query against the HTTP based Subject Heading URI for WWW
- SPARQL Query (with reasoning via inference rule for owl:sameAs) against the URN based Subject Heading URI for WWW
- SPARQL Query (*without* reasoning via inference rule for owl:sameAs) against the URN based Subject Heading URI for WWW
Observations:
The SPARQL queries against the Graph generated and automatically populated by the Sponger reveal -- without human intervention-- that: "info:lc/authorities/sh95000541", is just an alternative name for < xmlns="http" id.loc.gov="id.loc.gov" authorities="authorities" sh95000541="sh95000541" concept="concept">, and that the graph produced by LCSH is self-describing enough for an OWL reasoner to figure this all out courtesy of the owl:sameAs property :-).
Hopefully, this post also provides a simple example of how OWL facilitates "Reasonable Linked Data".
Blogs are so informative where we get lots of information on any topic. Nice job keep it up!!
Posted by: HR Dissertation | November 04, 2009 at 10:07 AM