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Re: DTDs, W3C Schemas, RELAX NG, Schematron?

• To: "John Cowan" <jcowan@r...>, "Betty Harvey" <harvey@e...>
• Subject: Re: DTDs, W3C Schemas, RELAX NG, Schematron?
• From: "James Clark" <jjc@j...>
• Date: Fri, 24 May 2002 16:08:40 +0700
• Cc: "tariq abdur-rahim" <ecliptoid330@y...>, <xml-dev@l...>
• References: <200205231616.MAA11258@m...>

> Betty Harvey scripsit:
>
> > I personally believe that DTDs still have a future. 4 years ago they
> > started chiselling the gravestone for DTD's and yet 4 years later new
DTDs
> > are still being developed and there is still controversy surrounding the
> > various schema languages.  Most commercial tools still support DTDs.
>
> Insofar as DTDs are used to describe content models and attribute
information,
> I agree.  It is very slick to take a stand-alone DTD, convert it to RNG
> with DTDinst (which carefully preserves readability), and then use Jing
> to validate against incoming documents.

What I think is also slick, is that having automatically converted your DTD
to RELAX NG, you can then maintain it in RELAX NG, perhaps upgrading it to
use datatypes, and then use Trang
(http://www.thaiopensource.com/relaxng/trang.html) to convert it back to a
DTD, with anything that DTDs cannot support being approximated as best as
possible (i.e. typed data in content would turn back into PCDATA).
Parameter entities, multiple files, comments etc are preserved through this
roundtrip.

Maintaining your DTDs in RELAX NG format has significant advantages.  It's
easy to write XSLT to do various sanity checks on your DTD or to do
transformations safely and reliably (e.g. generating a version with element
and attribute names in a different language).  It's easy to generate nice
documentation automatically.  You can add structured documentation in XML
into the schema so that your DTDs and documentation are generated from the
same file.  And, in the vaporware department, when I extend Trang to have an
output module for XML Schema, you will be able to get an XML Schema for free
too.

If anybody is looking for a fun project, you might want to look at writing a
program to generate an SVG diagram of a schema from RELAX NG.

James

• References:
  • Re: DTDs, W3C Schemas, RELAX NG, Schematron?
    • From: John Cowan <jcowan@r...>

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