Mark Wahl of Informed Control led a session on identity schemas and how to deal with them. People reinvent schemas, they use different labels for the same data, there's problems bringing these various schemas together. Moreover, a community shouldn't have to go to a standards body every time they have an identity data storage problem. He brings up Ham Radio operators. If they want to use call signs as identifiers, who should decide how that fits in?
X.509 dealt with many of these issues. There are well known problems with X.509 collapsing under its own weight. Today's directories solve these problems with metadirectories, but who on the Internet could run such a metadirectory? Mappings are ugly, even with metadirectories because you still have to agree on the mapping. That's very political.
The syntactic problem is largely solved thanks to XML, but the semantics are problematic since they are often hard coded into the application.
Hub and spoke federation systems begin to form shared schemas.