We should define some rules for URIs or at least examples and best practive for different use cases.

One problem is the detection of well defined namespaces through aggregating servers. An aggregating server is normally mapping the namespaces of the aggregated server into his own namespace table by adding a prefex to the orginial namespace e.g. the ServerUri.
If there is no rule to construct such a URI, a client to the aggregating server is not longer able to detect the known, well defined namespace in the underlying aggregated server.

This is a major problem with information model specifications. Clients need to be able to detect well known namespaces.