Hi Freek,
If the owner is part of the identifier (as I just suggested in my previous mail; e.g. identifier=glif.is:2678), and there is another mapping from owner (glif.is) to phonebook (e.g. https://idc.internet2.edu/ws/status.cgi), then each domain can only have one phone book.
I think that in both cases (domain + opaque local ID and attribute/value pairs including domain=) the owner is part of the ID. That seems to be necessary to avoid another level of indirection.
In Jeroen's proposal, each identifier is just a string, and there is a direct mapping from identifier to each phone book. So without the intermediate mapping of the identifier to owner to phonebook. The advantage is that a domain can have two phonebooks. E.g. the phonebook for glif.is:2678 may be https://idc.internet2.edu/ws/status.cgi. while the phonebook for glif.is:2679 may be http://glif.is/ws/status.cgi.
Something has to know that information for all of glif,is, right?
So Jeroen's proposal is even more flexible.
I don't agree that untyped, flat identifiers are more flexible. In our scheme, the opaque version could be: domain=glif.is, id=2678 But one could also have domain=glif.is, gole=foo domain=glif.is, node=rembrandt domain=glif, subdomain=something The attributed syntax allows you more flexibility to encode semantic info. martin