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Subject: Re: Separate treatments for System ID and others URI-References


/ Daniel Veillard <veillard@redhat.com> was heard to say:
|   C.f. sections 7.1 and 7.2 of 
|   http://www.oasis-open.org/committees/entity/spec-2001-08-06.html#s.semantics
| 
|   I don't understand the rationale for separating the processing
| of URI-References in external identifier from others URI-References.

Two reasons:

1. The external identifier has both public and system parts and this
requires the resolver to be more sophisticated. It has to handle
different prefer settings and the possibility of public as well as
system delegation. For the purposes of resolution, you cannot treat a
system identifier like a random URI.

You could, I suppose, treat a random URI like an external identifier
with a null public id, but that would make every resolution take into
account possibilities that cannot arise.

2. The external identifier catalog semantics are well understood and
have been used by the SGML and XML communities for years. It was a
requirement of the TC that the semantics of XML Catalogs in this
regard would be exactly the same as the semantics of TR9401.

General URI lookup is a new feature so it seemed reasonable to isolate
it.

|    http://www.w3.org/TR/REC-xml#NT-ExternalID
|    the system identifier is an URI reference...
| 
| If there is no public ID and doing just a system ID roslution, the processing
| is different than for what section 7.2 seems to think is a "normal"
| URI-Reference.

How so?

| I really don't see why two similar URI-Reference (assuming similar base)
| may lead to different resources when processed by the same software and
| coming from the same entity. This seems to break the very generic 
| nature of URI-references and I really can't see the point, maybe
| you can provide a rationale for this.

Because external identifiers must point to a very constrained set of
resource types. I doubt that, in practice, the same absolute URI is
ever used in an external identifier and in another context and you do
*not* want them mapped differently.

Actually, I doubt that this case of a duplicate URI ever occurs at
all.

                                        Be seeing you,
                                          norm

-- 
Norman.Walsh@Sun.COM   | Two starving men cannot be twice as hungry as
XML Standards Engineer | one; but two rascals can be ten times as
XML Technology Center  | vicious as one.--George Bernard Shaw
Sun Microsystems, Inc. | 


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