Re: re ERB discussion of public identifiers

	From: Peter Flynn <pflynn@curia.ucc.ie>
	Subject: Re: re ERB discussion of public identifiers

	Terry Allen writes:

	   Why require?  (a SYSTEM id)

	Because to go by current performance, processors and apps on the Web
	neither know nor care about PUBLIC indentifiers (with one or two
	obvious exclusions), and certainly wouldn't know where to go to broker
	a request for resolution.

I agree with Terry that this is theoretically suspect, but practical
considerations have made me side with Peter up till now. However,
Terry made a good point -- URNs will not be widely used for
publication until thereS is a widely implemented resolution base, so
there will be no need to require SYSTEM IDs as people will need them
and include them. Once at least one URN scheme is widely deployed,
then there may be no point in requiring a SYSTEM ID. I find this
market logic pretty convincing, but I can accept the compromise as
require SYSTEM IDs even though they may not be necessary.

	   Just say that the author has the two choices of
	   how to refer, by URL (SYSTEM) or URN (PUBLIC), or both. 

	This is exactly the problem I pointed out the other day. It is
	insufficient to allow both without indicating the sequence in which
	they should be tried, regardless of how any resolution is to be performed.

I think this point is important: even more importantly, the URN (FPI)
should take priority, if it is resolvable -- since URN resolution,
when applicable, has more options to produce the "best" copy -- since
it is constrained only by the identity restrictions of URNs, rather
than the location restrictions of SYSTEM identifiers.