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   Re: SUMMARY: XML Validation Issues (was: several threads)

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  • From: David Brownell <db@eng.sun.com>
  • To: Chris Lilley <chris@w3.org>
  • Date: Sun, 04 Apr 1999 22:31:42 -0700

Chris Lilley wrote:
> The assertion has been made that client-side validation is a performance
> load, compared to just parsing the dtd looking for fixed attributes etc;
> but no performance figures were made available. If someone has a parser
> they could instrument and provide some actual measurements on real-world
> data, that would help.

Have a look at Sun's XML parser package ... there's a cost
to validating, but the validating parser is as fast as many
other nonvalidating parsers.  That was one of the interesting
conclusions we drew last summer:  validation isn't all that
expensive.  The first several validating parsers just weren't
written with efficiency in mind; we were 10-20 times (!!) faster
than the others we compared against.

The extra costs are primarily in checking whether the content
model has been followed.  Checking other validity constraints
is pretty cheap.  It should be very easy to see just what code
kicks in differently in the validating and nonvalidating parsers;
look at the code, you'll see what I mean.

I've noticed something like a 10%-30% time price for validating;
it's also true that the validation code hasn't really been tuned
so it's likely the price can be reduced.  I've also seen XML
parsers that reduce such costs by not conforming to the XML spec,
which approach I won't endorse!  :-)

- Dave

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