There’s a school of thought that URIs should be opaque identifiers with no inherent meaning or structure. I think this is clearly a bad idea on the human-facing web, but it is more reasonable for computer-facing web services.
However, I’ve been generating a lot of RDF lately, trying to organize piles of metadata in AltLaw. I use URIs that have meaning to me, although they aren’t formally specified anywhere. I realized that a URI can represent a lot of information — not just the identity of a resource, but also its type, version, date, etc. — in a compact form. I can write code that manipulates URIs to get key information about a resource more quickly than I could by querying the RDF database.
Unfortunately, RDF query languages like SPARQL assume that URIs themselves are just pointers that do not contain any information. I could easily generate additional RDF statements containing all the same information encoded in the URI, but that would triple the size of my database and slow down my queries. (My experience so far with Sesame 2.0 is that complex queries are slow.)
What I need is a rule-based language for describing the structure of a URI and what it means. This would be similar to URI templates, and would map parts of the URI to RDF statements about that URI.
So if I make a statement about a resource at
http://altlaw.org/cases/US/1204
(note: not a real URI), the RDF database automatically infers the following (in Turtle syntax):
<http://altlaw.org/cases/US/2008-02-14/1204>
rdf:type <http://altlaw.org/rdf/Case> ;
dc:identifier "1204" ;
dc:jurisdiction "US" ;
dc:date "2008-02-14" .