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Re: XPath/XSLT 2.0 concerns

• To: "J.Pietschmann" <j3322ptm@y...>
• Subject: Re: XPath/XSLT 2.0 concerns
• From: Jeni Tennison <jeni@j...>
• Date: Thu, 3 Oct 2002 16:32:07 +0100
• Cc: xml-dev@l...
• In-reply-to: <3D9C4D3F.8000905@y...>
• Organization: Jeni Tennison Consulting Ltd
• References: <72RLYT04POLJXV95A7FBMJXRM82TRVT.3d9a6f4c@MChamp><144498584266.20021002103555@j...><3D9B0101.4020504@t...> <3D9B0CB4.6010207@p...><3D9B13F8.20608@e...> <12522921521.20021002172133@j...><3D9B2667.1050004@e...> <177584980918.20021003103553@j...><3D9C3ED2.5040508@y...> <12599360625.20021003143533@j...><3D9C4D3F.8000905@y...>
• Reply-to: Jeni Tennison <jeni@j...>

Hi Joerg,

>> Right, good point -- because the DTD information comes from the
>> source document. The stylesheet doesn't itself say "this is the DTD
>> that the source document uses". If it did, then it could make the
>> optimisations at compile time.
>
> Maybe add "possibility to declare a schema for source documents" to
> the XSLT2.0 requirements grab-bag? :-)

I think that it's there, or nearly there. See:

  http://www.w3.org/TR/xslt20/#section-Stylesheets-and-Schemas

and:
  
  http://www.w3.org/TR/xslt20/#import-schema

(and direct comments to public-qt-comments@w...).
  
>> Also, if you have compile-time optimisation of a 2.0 stylesheet or
>> query, effectively ignoring code that "couldn't possibly" be
>> relevant, you do have problems when you have a partially valid
>> document. If you want to be able to handle partial validity, you
>> can't really "optimise away" chunks of code because the basis of
>> your optimisation isn't necessarily true.
>
> I don't understand this. Currently, no XSLT processor I know of uses
> schema dependent optimisations, or even seriously thinks about this
> topic.

Sure, but there's a lot of stuff being put into XPath 2.0 precisely so
that XSLT processors *can* do this schema-dependent optimisation. I'm
trying to get at whether that stuff is worthwhile or not.

> And of course if someone did, it would only work on documents which
> are valid according to the schema. If a source XML document weren't
> valid, it would result in a fatal error even before the
> transformation starts.

OK.

So the picture that I have is that optimisation is probably only
useful if:

  - the schema of the source document is known at compile time
  - the stylesheet/query is compiled once, used many times
  - the source documents are completely valid

and even then, it's utility hasn't yet been proven empirically.

Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/

• Follow-Ups:
  • Re: XPath/XSLT 2.0 concerns
    • From: "J.Pietschmann" <j3322ptm@y...>

• References:
  • Re: XPath/XSLT 2.0 concerns
    • From: Mike Champion <mc@x...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Jeni Tennison <jeni@j...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Tim Bray <tbray@t...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Paul Prescod <paul@p...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Robin Berjon <robin.berjon@e...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Jeni Tennison <jeni@j...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Robin Berjon <robin.berjon@e...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Jeni Tennison <jeni@j...>
  • Re: XPath/XSLT 2.0 concerns
    • From: "J.Pietschmann" <j3322ptm@y...>
  • Re: XPath/XSLT 2.0 concerns
    • From: Jeni Tennison <jeni@j...>
  • Re: XPath/XSLT 2.0 concerns
    • From: "J.Pietschmann" <j3322ptm@y...>

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