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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 10:06:43 -0500

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?

My initial thoughts on this are that by itself a schema does not define
the "semantics" of a component.  For example,

<element name= "jdkdsfjkds">
        <restriction base= "string">
            <pattern value= "[a-zA-Z]+\d"/>

This is a legal schema declaration for an element, jdkdsfjkds. Now that
you've seen how jdkdsfjkds is declared, do you understand its
semantics?  My guess is that you do not.  In one of his messages,
Richard Lanyon referred to schemas as defining the "syntax" of an
element and not its semantics.  This makes sense to me.

Okay, so some questions for you:  

[1] Do you agree that, by themselves, schemas define just syntax and not

[2] A big question ... what is "semantics"?  Is semantics a universal
thing? Or is it an application-specific thing? That is, is there such a
thing as the semantics of jdkdsfjkds, regardless of what application is
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")

    Can we separate semantics and syntax?  
    Can define the syntax using the XML Schema 
    language and then apply different semantics, 
    depending upon the application?

       Application#1: element(jdkdsfjkds) + semantics(A)
       Application#2: element(jdkdsfjkds) + semantics(B) 

[4] How do we "add semantics" to a schema document?

I think that this is a very important and interesting issue.  I eagerly
await your thoughts on it.  /Roger


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