DTDs are just for validation (Re: Why Doesn't IE5 use the DTD to Validate?)
david at megginson.com
Thu Apr 1 12:56:51 BST 1999
Marcus Carr writes:
> To clarify, it's faster to process the DTD but not the instance
> than it is to process both, but it may be a marginal
> difference. Imagine using the DocBook DTD for the following
> <?xml version='1.0'?>
> <!DOCTYPE para PUBLIC "-//whatever the DocBook//DTD goes by//EN">
> <para>Baby Snakes.</para>
> Surely validation of the instance is a fairly minor issue, after
> the processor has had to plow through a large DTD?
> <InBigFatLetters>I'm not suggesting that XML documents should be
> validated client side</InBigFatLetters>, I'm questioning the wisdom
> of looking at the DTD at all if you're not putting it to any use.
> Surely the overhead of looking at the DTD outweighs the benefit
> (none) obtained in rendering the above example?
There *is* a potentially nasty problem lurking here: the DTD may
contain default values for attributes as well as validation
information. In the SGML version of DocBook, there is not a problem,
but what if the new version of DocBook had something like this?
xmlns CDATA #FIXED "http://www.oasis-open.org/docbook/">
I suspect that industry practice will be always to run XML through a
normaliser before publishing, so that the attribute default values get
plugged right into the instance.
All the best,
David Megginson david at megginson.com
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