[entity-resolution-comment] uri vs. system confusion

[Mark Johnson <mrj@debian.org>]

Hi All,

In working to develop a robust xml catalog system for Debian that's
consistent with the OASIS XML Catalogs spec, I find that I'm still a
bit confused about the distinction between the uri-based elements and
the system-based elements.

To get to the point:

  The spec doesn't clearly explain the distinction between the two,
  and, furthermore, doesn't provide any usage recommendations.

For example, here are a couple related points/questions:

A. The <rewriteURI> example given in 4.3 implies that not only is the
   prefix rewritten, but also that the intended document/entity is also
   included in the 'rewritePrefix' attribute. Put another way, the
   _complete_ URI is rewritten, and not just the prefix.

   If this is indeed the intended usage, perhaps the 'rewritePrefix'
   attribute should be changed to 'rewriteURIString' or something of
   the sort.

B. Given Paul Grosso's response (below) to a similar inquiry, 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? 

   If so, a clarification in the spec on this point would be very
   helpful. In discussions with fellow Debian XML/SGML developers, I
   find that this is a common source of confusion when attempting to
   grok the XML Catalogs spec in all its fullness:)

C. In 4.2 of the spec, the opening paragraph states:

   "Other URI references, for example namespace names, stylesheets,
    included files, graphics, and hypertext references, simply
    identify other resources. The input to a resolver that locates
    resources is simply the original URI reference."

    I find this confusing, as well. For example, to remap the URI that
    identifies a file within the current DocBook XSL stylesheet, I'd
    want to use <rewriteSystem .../> to point to the local filesystem
    like so:

<rewriteSystem 
  systemIdStartString="http://docbook.sourceforge.net/release/xsl/current/";
  rewritePrefix="file:///usr/share/sgml/docbook/stylesheet/xsl/nwalsh/"/>

    rather than using <rewriteURI.../>. But the text of the paragraph
    implies that <rewriteURI.../> should be used. 

    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...

FWIW, I recently joined the Entity Resolution TC (hence a prospective
member), so I'll continue to request that the spec clarify these, and
related issues - even if I can't yet cast a vote :-)

Thanks,
Mark


======================================================================
 Paul Grosso's response of Mon, 28 Oct 2002 [1] to an older message
 that Norm reposted:

David Brownell:

     >> - I really don't see any need to have both the "uri" and
     >> "systemId" sets of elements.

Paul's response:

     "The use of systemId is expressly to model production [75],
      ExternalID, of the XML spec.  This seems like good architecture
      to me.

      XML has no concept of a URI.  It only has a concept of
      ExternalID with a SystemLiteral."

======================================================================


[1] http://lists.oasis-open.org/archives/entity-resolution/200210/msg00013.html
-- 
_____________________________________
Mark Johnson        <mark@dulug.duke.edu>
Debian XML/SGML     <mrj@debian.org>
Home Page:          <http://dulug.duke.edu/~mark/>
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