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Subject: Re: XML-DATA vs. W3C's XML Schema working draft
From: Ronald Bourret <[log in to unmask]>
Reply-To:General discussion of Extensible Markup Language <[log in to unmask]>
Date:Fri, 6 Aug 1999 10:26:58 +0200

text/plain (14 lines)

Warren Wilson wrote:

> I'm an analyst trying to understand how XML is developing; can
> someone explain the relationship between Microsoft's XML-Data
> proposal and the W3C's XML Schema, now apparently in
> working-draft status?

Conceptually, they are not very different -- both (along with the other schema proposals SOX, DCD, and DDML) are trying to replace DTDs with an instance syntax. That is, they define an XML language that does the same thing as DTDs: defines elements, attributes, and so on.

For the most common operations -- defining elements and attributes and assigning data types (integer, date, etc.) to attributes and PCDATA-only elements -- both are technically very similar. For more exotic operations -- inheritance, reusing definitions from other schemas, etc. -- they differ in both scope and technique.  XML Schema offers more features than XML-Data Reduced (the part of XML-Data implemented by IE 5.0); it is not known how these will evolve in future drafts.

The most significant difference between the two is simply that XML-Data Reduced is implemented and XML Schema is not. However, many people seem to be waiting for XML Schema to become a recommendation before starting any schema work. When that happens, I suspect you will see a lot of software that uses schemas. I also suspect that XML-Data, as well as the other schema proposals, will largely fade away in favor of the standard.

-- Ron Bourret

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