CATALOGs and stylesheets

[David Seibert]

That sounds great, and mixes well with the PI approach.  Authors who want a
simple approach can just enclose the stylesheet URL in a PI inside the XML
document.  More sophisticated authors can do the same, and then label the
entire document with a single catalog URL, and the separate chunks with
different URLs.  (I haven't read the CATALOG extension, so I hope that I am
interpreting David's remarks correctly).

The sophisticated server could give the full catalog entry to sophisticated
clients, who would negotiate what to send; they would then presumably parse
the PI (they need to do this to deal with simple servers) and realize that they
already had the stylesheet.  Unsophisticated clients could just get the XML
text by default if they requested the base document, and  then request the
remaining chunks that they wanted.  Thus, the presence of the catalog could
be made transparent to unsophisticated clients.

This separation of the PI and catalog mechanisms (keeping one internal to
the XML document and the other external) allows simple clients and servers to
peacefully coexist with sophisticated ones, with graceful degradation of
functionality.  It's probably more appropriate as well, since clients
sophisticated enough to deal with the catalog should realize that the
document is really the whole collection of files, not just the XML file.  Is there
a compelling argument to make catalogs visible to users?

Regards,

David Seibert

----------
From: 	David Durand
Sent: 	Wednesday, March 19, 1997 9:05 AM
To: 	xml-dev at ic.ac.uk
Subject: 	CATALOGs and stylesheets

  There was a proposed CATALOG extension (even imnplemented, I think) for a
DOCUMENT(?) keyword that stated the starting for which the catalog applies.
With delegation this presents an alternative mechanism that will not be
fooled by mytery URLs. Each document with "attachments" has a catalog that
gives its URL and gives its DTD and stylesheet(s). Delegation is used to
make catalog management bearable for files that share public Identifiers,
so that common stuff resides in a common catalog.

   Then the URL that you send is the CATALOG URL, not the document URL --
and you get a whole directory of the stuff you might need, with the
potential for any mapping you want from URIs to URLs.

   I'm not a CATALOG zealot, but it's an approach that bears consideration.

  -- David

_________________________________________
David Durand              dgd at cs.bu.edu  \  david at dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
--------------------------------------------\  http://dynamicDiagrams.com/
MAPA: mapping for the WWW                    \__________________________



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