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   Re: XML Schemas: Best Practices

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  • From: "Roger L. Costello" <costello@mitre.org>
  • To: xml-dev@lists.xml.org
  • Date: Wed, 22 Nov 2000 16:17:42 -0500

I am forwarding this from Mike Ripley:

At 10:06 AM -0500 11/22/00, Roger L. Costello wrote:
>Hi Folks,
>I would like to move on to the next issue in our schema design list.
>Issue: How do we define the semantics of schema components?

Big topic area that I could talk about for hours - lucky for everyone 
I am restricted to e-mail and the amount of time I have to put into 
typing a reply...

>[1] Do you agree that, by themselves, schemas define just syntax and

No, it's not that black and white.  If I nest things a certain way, 
or define a set of enumerated values, or define a complex type, I can 
provide lots of information that help define the semantics of a 
particular element.  Can we completely describe the semantics with 
XML Schemas alone?  No, otherwise we wouldn't be having this 

>[2] A big question ... what is "semantics"?  Is semantics a universal
>thing? Or is it an application-specific thing? That is, is there such
>thing as the semantics of jdkdsfjkds, regardless of what application
>using it?  Or, is the semantics of jdkdsfjkds dependent upon the
>application that is using it? (i.e., "in this context jdkdsfjkds means
>xxx, whereas in that context it means yyy")

Both forms of semantics exist.  IMHO, application specific semantics 
are what keep getting us in trouble with regards to data 
interoperability.  Hence the drive for ontologies, common data 
environments, standardized database schemas, common data models, etc.

What should be a Best Practice?  I'm in strong favor of universal 
semantics.  It's very difficult to implement, but it's what we should 
try to do.

>    Can we separate semantics and syntax? 
>    Can define the syntax using the XML Schema
>    language and then apply different semantics,
>    depending upon the application?
>    Example.
>       Application#1: element(jdkdsfjkds) + semantics(A)
>       Application#2: element(jdkdsfjkds) + semantics(B)

This is a recurring theme you have - why?



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