I think that originally "printer-uri" was going to be a "virtual"
attribute,
as you thought. But later (last Fall?) we changed the Model and
Protocol
document so that the "printer-uri" attribute was required to be
supplied
by the client and include in the operation attribute group in the
IPP packet
(which is defined by the application/ipp MIME type). The thinking
was that we wanted the IPP packet and MIME type to be independent
of the transport. So that we could send IPP over any transport,
such
as SMTP or FTP, for examples.
OK. So we are saying that the URIs IN the protocol are NOT to be used as
transport adresses. They are in effect opaque cookies that the client must
do nothing with except send them back to the printer. They are really
job-name and printer-name. Either that or we explicitly state that these
fields only make sense in an HTTP-enabled environment (they cannot therefore
be mandatory for a universal protocol).