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   Re: [xml-dev] XML Catalogs and Public Ids

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Leigh Dodds scripsit:

> [A]ccording to Section 7.1.2 of the spec if a system identifier can be matched 
> in the catalog then that will always be used; an accompanying public 
> identifier is only used as a fallback if the system id doesn't match 
> (or is unavailable) and the prefer setting is "public".

So far so correct.

> So public ids are 
> only useful if the system identifier isn't available.

Not so.  A system identifier matches only if there is a system, rewriteSystem,
or delegateSystem entry in the catalog.  So if there are none of these,
then as long as prefer="public" is set (which it should always be), then
public, rewritePublic, and delegatePublic rules are applied.

The setting prefer="system" is really only useful for SGML backward
compatibility.  Historically, the SGML system id was generally a local one,
whereas the public id was meant to be universal.  XML has made the system id
universal instead; nevertheless, XML Catalogs were meant to be semantically
identical to TR9401 catalogs.

> Given that you 
> have to provide both in XML, public ids seem pretty redundant.

There are two cases in which a public id can exist without a system id:
in a NOTATION declaration, and after delegating to a new catalog via
delegatePublic (in which case the original system id is discarded).
> Toying with the command-line resolver application shows behaviour consistent 
> with this reading.
> Everything I've read up to now set me up to expect the following: that 
> Public Ids would be preferred and that System Ids would be the fallback.
> What am I missing?
> [1].
> https://www.oasis-open.org/committees/entity/specs/cs-entity-xml-catalogs-1.0.html
> [2]. http://xml.apache.org/commons/
> [3].
> https://www.oasis-open.org/committees/entity/specs/cs-entity-xml-catalogs-1.0.html#s.ext.resx
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John Cowan  jcowan@reutershealth.com  www.ccil.org/~cowan  www.reutershealth.com
"If I have seen farther than others, it is because I was standing on
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