Re: [entity-resolution] Re: uri vs. system confusion

[Paul Grosso <pgrosso@arbortext.com>]

At 12:37 2003 02 08 -0700, Mark Johnson wrote:
>John (and others),
>
>(BTW, this discussion started with my post [1] to the
>entity-resolution-comment list.)
>
>After reading the relevant section of the XML spec (4.2.2), I still
>find redundancy in using both system-based and uri-based elements. The
>problem lies in the fact that the XML spec defines 'SystemLiteral' as
>a URI, thereby _not_ limiting its form to that of a URL.
>
>Furthermore, (external) ENTITY declarations and NOTATION declarations
>(XML 4.7) both make use of the form of an ExternalID, i.e. a
>SystemLiteral.
>
>And, as mentioned above, the SystemLiteral is defined as a URI (not a
>URL). From section 4.2.2 of the XML spec:
>
>   [Definition: The SystemLiteral is called the entity's system
>   identifier. It is a URI reference (as defined in [IETF RFC 2396],
>   updated by [IETF RFC 2732]), meant to be dereferenced to obtain
>   input for the XML processor to construct the entity's replacement
>   text.]
>
>Since: 
>
>a. all relevant non-public references are required to be
>   SystemLiterals, and,
>
>b. all SystemLiterals are URIs,
>
>Then:
>
>1.  all SYSTEM ids should be treated as URIs, and nothing less.

I don't follow your reasoning.

Yes, XML says that system ids are URIs.  That doesn't say that
all URIs are system ids.  In XML, a system id is one of a pair
of identifiers--the system id and the (optional) public id--that
make up an external identifier of an external entity reference.

It's these system ids that are matched against the catalog entries
that refer to system ids.

Anything else in an XML document that the application may have
reason to believe is a URI reference is not a system id.  These
are the things that are matched against the catalog entries that
refer to URIs.

>Therefore all SYSTEM references should make use of the uri-based
>elements - and not the system-based elements.

I don't see the "therefore" in your argument.

>Furthermore, use of uri, rewriteURI, and delegateURI in lieu of the
>system, rewriteSystem, and delegateSystem elements seems to be
>consistent with Production 75 of the XML spec.
>
>So I don't see why the system-based elements are needed at all.
>
>   (I can't help but wonder I'm missing something here, as I now feel
>    like I understand the issue...)

You appear to have company in that there are others that disagree
with the distinction we have decided to make in the spec.  As far
as I can tell, this disagreement has gone on for a while and neither
side seems to come closer to changing its mind.  (I am still firmly
on the side that cannot see why folks cannot see the difference
between system ids and non-system id URIs, but smart people are on
the other side too.)

paul

>Clarification, anyone?
>
>Thanks,
>Mark
>
>[1] http://lists.oasis-open.org/archives/entity-resolution-comment/200302/msg00000.html
>
>On Friday, February 7, John Cowan wrote:
>> Mark Johnson scripsit:
>>
>> > [...] I'm still a bit confused about the distinction between the 
>> > uri-based elements and the system-based elements.
>> 
>> In a word, the system-based elements are used only when an XML parser is
>> processing ENTITY and NOTATION declarations in the DTD.  The URI-based
>> elements are used for all other lookups.
>>
>>
>> > B. [...] another implied usage is IMO that SYSTEM Ids get remapped
>> >     _only_ via a <rewriteSystem> element, and never via the 
>> >     <rewriteURI> element. (This despite the fact that all system 
>> >     identifiers are URIs.)
>> > 
>> >    Is this the intended usage? 
>> 
>> Yes.
>>
>> >     Does the reason for using <rewriteURI.../> have something to do
>> >     with the fact that the stylesheet URI does NOT appear in the XML 
>> >     document, and is therefore not restricted by the ExternalID as
>> >     SystemLiteral constraint as per the XML spec? Again, any 
>> >     clarification here would be greatly appreciated..
>> 
>> Just so.
>
>-- 
>_____________________________________
>Mark Johnson        <mark@dulug.duke.edu>
>Debian XML/SGML     <mrj@debian.org>
>Home Page:          <http://dulug.duke.edu/~mark/>
>GPG fp: 50DF A22D 5119 3485 E9E4  89B2 BCBC B2C8 2BE2 FE81
>
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