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   Re: [xml-dev] content model question

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Rick, Thank you for this really helpful reply.
Morgan Cundiff

On Mon, 8 Apr 2002, Rick Jelliffe wrote:

> From: "Morgan V. Cundiff" <mcundiff@loc.gov>
> > Thanks for your reply. I was afraid this might be the case. (It is a given
> > that our project will use XML Schema and not one of the alternatives.)
> The way to solve this kind of problems if you must use XML Schemas is 
> to use the <annotation><appinfo> elements. Then you embed a Schematron 
> assertion. Appinfo was provided to allow constraints that go beyond XML
> Schemas. 
> See Eddie Robertsson's article "Combining the power of W3C 
> XML Schema and Schematron" at
> http://www.topologi.com/public/Schtrn_XSD/Paper.html
> To validate, you can make you a script using three XSLT transforms and
> open source code (one to extract the constraints, one to compile the constraints,
> one to run the constraints) or, if you are on Windows, download the free
> Topologi Schematron Validator at http://www.topologi.com/
> This kind of content model was available in SGML:
>     <!ELEMENT myelement ( #PCDATA, subelement1, subelement2)>
> however that kind of content model is not available in XML DTDs or XML Schemas.
> One good reason is that usually it means that you have some structure that you want
> to elide: that the initial textblob has some significance but you don't want to
> tag it. This goes against one thrust in XML, that terseness is not catered for:
> if you need terser markup, you need to go away from W3C DBMS approaches more
> to the publishing side of the family (ISO, OASIS) of markup standards: RELAX NG,
> DSDL, SGML etc.   
> Having said that it may be bad modeling, it can undoubtedly be idiomatic markup:
> blocking PCDATA from between certain elements may fit in with the way we
> like to think about things. And who says terseness is always of minimal importance
> anyway?  The XML goal of terseness is primarily about documents being transmitted
> over the WWW where other layers are known, not documents being created or maintained
> or read.   Two well-known document types which have some kind of data restrictions
> are the original TEI and XSLT AFAIK. 
> Cheers
> Rick Jelliffe
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