URI explosion

The undetermined meaning of relative URI references

Prelude: What is a Namespace? The W3C had a major struggle over the use of namespaces in XHTML. One namespace per DTD? Or one for XHTML as a whole? Eventually, the one namespace for the entire vocabulary approach won, but no real definition of 'namespace' emerged.
URI references vs. absolute URIs The W3C halted many activities for a brief period this summer because of deadlock over the meaning, if any, of relative URI references in namespaces.
Why they were included URI references allow the inclusion of fragment identifiers, like #location, a useful feature for creating multiple different namespaces associated with a single URI.
The absolutization problem Because URI references include the possibility of relative URLs, namespaces using URIs might change identifier if the document moved between contexts. On top of that, the mechanisms for converting relative URI references to absolute URIs may change between URI schemes.