URLs and URIs (was XLink and mixed vocabulary design)

 (Henrik Martensson) writes:
>I would be interested in seeing your take on a multiended link that has
>no collection of exposed URIs. The XHTML 2.0 img element does not
>qualify, I believe, because, well, it does have a collection of
>attributes, and their values are exposed.

This point is worth addressing, whatever the context.

I have no qualms about exposing URLs.  People are familiar with URLs,
and the notion of pointing to something using a URL is well-understood.

I draw the line at exposing URIs when used as identifiers for purposes
other than retrieval.  This seems to be the W3C's universal escape
hatch, whether for namespaces, RDF, or XLink.  Unfortunately, the
combination of opacity, confusion with URLs, and cross-referencing
difficulty as their number increases seems to produce as much chaos as
it resolves.

The distinction between URLs and URIs seems to be one worth emphasizing
in practice, even if the standards bodies are doing their best to blur.