Of Presidents and Ontologies

Beyond its sheer content interest - providing RDF description of the new(?) US President - this article is also a good introduction to Tag URIs in the following terms:

Under no circumstance should a Semantic Web application attempt to derive meaning from a URI string alone. Tag URIs have exactly one purpose: to allow us to quickly, consistently create unique identifiers that aren't intended to be de-referenced and without needing to register a URI scheme with anyone.

Tag URIs go in a direction opposite to PSIs, since they can't be de-referenced on the Web. So they are supposed to be sort of "self-explaining" identifiers.