SUMMARY: XML Validation Issues (was: several threads)

Tim Bray tbray at
Thu Apr 8 17:22:32 BST 1999

At 01:38 AM 4/7/99 +0200, Chris Lilley wrote:

I mostly agree with Chris, but a couple of notes.

>True, but the assertion was made that validation should never be
>required because of the performance load (compared to parsing the dtd
>including external subsets, but not validating). Which implies, if there
>were negligible performance load, them whould validation be a desirable

It still depends.  In lots of scenarios, validation isn't worth even
an extra 1% investment in time.  In lots of scenarios, there's no DTD!
Having said that, a guaranteed-lightweight validation protocol would
be nice.

>I didn't like it much either, but it seemed to be, on inspection, what
>the XML spec said.
>James Clark seemed to agree, which was a good sign. But I recently heard
>Tim Bray and CMSQ say that no, it doesn't mean that at all 

What the spec itself says is more important than what any of us
individuals say.  I really don't think you can find justification
in the spec for the notion that the existence of a <!DOCTYPE is
a signal requiring any kind of action.

>(not to UI designers, provide two
>separate icons for "validate" and "check wf" )

Yes!  IE5 has a nice validation capability, but no way (that I've 
found) for the user to invoke it.  Is there one?

>Next question, should there be (in other words, is this something that
>should be in the document instance).

Good question; I can see both sides.  But in fact, Chris, I think what's
motivating you here is less a concern for forcing validation than a 
concern for forcing the use of the external DTD for entity declarations
& attribute defaults and so on.  Which is fine; but I think there are
2 separate questions here:

 - should a document be able to ask for validation
 - should a document be able to ask for guaranteed reading of all
   external entities

Related but distinct. -Tim

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