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   Re: DTDs vs Schemas

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  • From: Sam Hunting <sam_hunting@yahoo.com>
  • To: Rick Jelliffe <ricko@allette.com.au>, xml-dev@lists.xml.org
  • Date: Thu, 28 Dec 2000 09:47:55 -0800 (PST)

[rick jelliffe]
> Unlike DTDs, W3C XML Schemas uses XML element syntax, are
> namespace-aware and provide the kinds of datatyping that people
> expect.

A balanced summary. Since this discussion began as advice to a newbie,
let me add that being (W3C) namespace "aware" is not without
controversy. Some regard the Namespace Recommendation as being, to put
it politely, underspecified.

W3C schemas are very complex. Further, their validity is not direectly
visible by reading the markup: many of the spec's semantic constraints
are expressed only in the prose of the specification. Finally, W3C
schemas cannot be understood by reading the specification alone:
schemas are "layered" over other specifications (for example,

As a result of this complexity, it's likely that W3C schemas will
require a development environment (unlike DTDs, which can be developed
using a text editor and a few public domain tools).

So I suppose that W3C schema could be viewed as having made a market
for schema development tools. Whether this is a good thing, or a bad
thing, from the standpoint of interoperable information is left as an
exercise for the reader.

The bottom line is that the W3C Schema specification is about as
"simple" as the original SGML ISO standard. Whether it is as robust and
stable remains to be seen.


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