What are schemata

Simon St.Laurent SimonStL at classic.msn.com
Mon Jun 1 02:12:50 BST 1998

Marcus Carr wrote:
>I would have thought that support for compound documents 
>and partial validation would involve much more than the 
>relatively simple current goals of Xschema.

Will XSchema, by itself, provide support for compound documents and partial 
validation? No.

Will XSchema make such things easier?  Yes.  As long as we stay out of the 
morass of questions like 'what is a document?', we don't need to worry about 
root elements and other charming relics.

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. 

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 

I don't see us defining any more than a very simple mechanism (if indeed we 
define a mechanism) in XSchema 1.0, however.  All we've committed to doing is 
providing a schema with a transformation to a DTD.

Simon St.Laurent
Dynamic HTML: A Primer / XML: A Primer / Cookies

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