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   Re: What are schemata

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  • From: Marcus Carr <mrc@allette.com.au>
  • To: xml-dev@ic.ac.uk
  • Date: Mon, 01 Jun 1998 11:22:57 +1000

Simon St.Laurent wrote:

> I think that moving from a DTD-based system, where behavior has been
> prescribed for SGML parsers and is effectively unchangeable (the glories of
> the installed base), to a new system that will necessarily require a different
> mechanism for connecting to documents, will require a reconsideration of the
> questions regarding the connection of a schema to its documents.

I'm still having a bit of a hard time getting my head around what the new
mechanism for connecting to documents might involve. Are suggesting the schema (or
multiple schemata) would be invoked numerous times based on the existence of a
particular element, for instance? That would certainly make sense for processing
fragments in an otherwise only well formed document.

> In short, XSchema itself won't answer the question - all it defines is
> elements and attributes, with no grave concern for which one is the root.  The
> declaration connecting the schema to the document (or whatever mechanism makes
> that connection) has the opportunity to present partial schemas for partial
> documents, compound schemas for compound documents.  That intelligence must
> reside in the application, and I hope it will be specified in a different
> standard.

The ability to feed multiple documents with arbitrary root elements to a
persistent process combined with the ability to pick an element out of an
otherwise only well formed document is already available with OmniMark. I agree
that it would open things up if you could move some of the intelligence out of the
application and into the data/XSchema, but I'm still not clear how XSchema will
accomplish this without becomming very complex. If the intention is to support
such things as multiple "XSchemettes" for fragments as well as an overall XSchema
that may be applied to the document as a whole, aren't we flying awfully close to
SUBDOC? Would the generation of the XSchema sometimes be the result of validating
the documents (for want of a better phrase) against the DTD and combining
information that with some other logic?

I hope this doesn't sound too disjointed; I'm just trying to understand when,
where and how in the process the XSchema may be implemented.


Marcus Carr                  email:  mrc@allette.com.au
Allette Systems (Australia)  email:  info@allette.com.au
Level 10, 91 York Street     www:    http://www.allette.com.au
Sydney 2000 NSW Australia    phone:  +61 2 9262 4777
                             fax:    +61 2 9262 4774

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