Re: DTD Files !

David Carlisle is correct that XSL can be used for many kinds of
validation, more kinds in fact than DTDs. One of its advantages in such
cases is that it can do a kind of "loose" validation, as opposed to being
just a "go/no-go" gauge, which is what DTDs amount to (either the document
conforms, or it doesn't).

Nevertheless, there are cases where DTDs are very useful (and I don't think
David has tried to make the argument that DTDs are never useful -- only
that XSL, and/or other validation techniques, can be used for many types of
validation).

One thing DTDs are useful for (that other contributors to this thread have
mentioned) is the configuration of a structured editor, which actually
constrains the user's data entry to assure that anything created will
conform to the necessary model. When using such an editor, only elements
and attributes explicitly allowed by the DTD can be inserted in a given
place. Especially when non-experts in XML or the document model are writing
content, and when documents are large and complex, this is *much* easier
than creating the stuff and then doing validation on it in batch mode
(whether by using a DTD or by another method).

So far I haven't seen a structured editor that can use XSL validation like
this. Actually an XSL stylesheet would be a pretty difficult thing to wire
into this type of application (if not impossible), although I dare say the
schemas that Rick Jelliffe's Schematron uses to build its stylesheets (or a
subset of them), might work. When XML Schema is done, it's expected one of
its common use cases will be for this kind of thing. So far, the only
editors I know of that work like this (XMetaL, Excosoft Documentor,
Arbortext, WordPerfect etc.) all start with DTDs.

Another thing DTDs are useful for, in my experience, is in learning XML,
since they can give a good sense of the structuring possibilities of the
language -- something quite new, for example, to HTML users.

But this is really out of scope for this list -- it should really be on
XML-L, where probably a greater portion of the readership would find it
useful or interesting.

--Wendell


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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