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Re: Argh...Entities

From: <Noah_Mendelsohn/CAM/Lotus@lotus.com>
Date: Tue, 11 May 1999 20:49:16 GMT
To: "Simon St.Laurent" <simonstl@simonstl.com>
Cc: Paul Prescod <paul@prescod.net>, www-xml-schema-comments@w3.org
Message-ID: <OFE58DDE69.2529C624-ON8525676E.00711714@lotus.com>
Thank you both for your notes.  One other perspective to add:

The schemas WG has given very serious consideration to the view that 
validity constraints should be somehow separated from anything in the 
schema that affects content.  Entities do affect content and could be 
eliminated or perhaps "put in a box" as you suggest.

The more difficult case, I think, is default values for attributes.  These 
too affect content (and in the case of default values for namespace 
attributes can affect the deeper meaning of the document structure.) 
Anyway, we've heard strong opinions expressed that (1) default values for 
attributes are an important feature of any replacement for DTDs and (2) 
that it would be very cumbersome to define the default values somewhere 
that is far removed from the declaration of the attribute itself.  The 
natural place to introduce a default does seem to be on the attribute 

So, depending on how you feel about that analysis of attribute values, 
pandora's box is then open.  The schema can afffect the contents of a 
standalone=no document.  Having, with regrets, crossed that bridge, does 
that change the net tradeoff on entities?  Maybe.   The standalone=no 
document is already potentially dependent on the schema for other reasons, 
I.e. attribute defaults.  Now the question is:  be a proper superset of 
DTD, including questionable features, or leave out entities?

Anyway, these are some of the issues we wrestled with.  You can see where 
we landed this time.  Thanks again for the feedback.


"Simon St.Laurent" <simonstl@ on 05/11/99 04:18:32 PM

To:     Paul Prescod <paul@prescod.net>, Noah_Mendelsohn/CAM/Lotus@lotus.com
cc:     www-xml-schema-comments@w3.org 
From:   "Simon St.Laurent"
Originally from: 
Date:   05/11/99 04:22:49 PM
Subject:        Re: Argh...Entities

At 02:43 PM 5/11/99 -0500, Paul Prescod wrote:
>Noah_Mendelsohn/CAM/Lotus@lotus.com wrote:
>> It's my impression that at least some of the editors share the
>> reservations expressed about various aspects of the entity mechanisms, 
>> are thus reluctant to perpetuate them as we did in the new design.  It
>> does appear that failing to do so would restrict one's ability to 
>> arbitrary DTD's into equivalent schemas, and would entail a change of 
>> requirements document along with an associated change in the design. So
>> it's a tradeoff, and I don't think we've finally settled which way to 
>> Your opinions are much appreciated.
>Thanks for your message. I do think that the requirements should either 
>changed or interpreted as: "allow the expression of the same constraints
>as those expressed by DTDs."

Agreed.  If necessary, maybe you could move entities into their own
separate box, somewhat like has been done for data types.  I won't mind if
the W3C specifies a new way to provide the functionality that entities
provide today, but I'd very much like to see those capabilities separated
from the constraints end of schemas. 

Simon St.Laurent
XML: A Primer / Building XML Applications (June)
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Received on Tuesday, 11 May 1999 16:45:33 UTC

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