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RE: XQuery -- Reinventing the Wheel?

• From: Evan Lenz <elenz@x...>
• To: Kimbro Staken <kstaken@d...>,Uche Ogbuji <uche.ogbuji@f...>
• Date: Wed, 21 Feb 2001 18:51:43 -0800

Kimbro Staken wrote:
> I believe Evan's major point
> is just that the majority of XQuery syntax can be easily mapped to XSL-T
> and that creating an entirely new syntax may not be the proper thing to
> do.

Yes, and not only a new syntax, but a new semantics and data model that look
*so* much like XPath/XSLT, just not quite the same.

> Clearly XSLT as it stands now is not fully sufficient to act as a
> query language.

I think this is so primarily with regard to its lack of support for
datatypes (apart from the four XPath datatypes). Of course, both the XSLT
and XPath 2.0 requirements talk about XML Schema datatypes. Regarding XML
Schema: Structures, I tend to sympathize with Rick Jelliffe. I thought XML
was supposed to be self-describing, serializable, etc. That's another story.
In any case, I think there should be some sort of layering with regard to
what complexity is lumped onto XPath a la XML Schemas. I still have a lot to
learn there (and I don't think I'm the only one ;)

> It seems though, that the changes required would be
> minor compared to having to deal with an entirely new language or even
> worse two new languages once the XQuery XML mapping is added.

Yes, especially when you consider that a good deal of the outstanding issues
with regard to XSLT's use as a query language are also outstanding issues
for XQuery.

> I certainly don't see current XSLT implementations suddenly becoming query
> engines, performance just isn't good enough. However, a specialized XSLT
> engine that implements a slightly modified spec and has an optimizer to
> utilize indexes might be a much simpler way to go. Regardless it would
> certainly be able to leverage the vast majority of the work already put
> into XSLT vs. starting from scratch on XQuery implementations. The more
> I think about it the more I find it a compelling idea but I just have to
> wonder if it can be made to perform well enough.

And this is where my particular expertise runs out. The XQuery people must
think their language has the ability to perform well as a query language. If
XSLT can't perform well in comparison to XQuery, then it would be due to
some combination of the pattern-matching template rules and the XPath axes
that don't have abbreviated syntaxes (BTW, this is a particularly weird way
to specify a language, historically tied to XQL, etc.). I personally think
that template rules are perfect for XML processing, and it seems that
XQuery's filter() function tries to achieve a small subset of that
functionality, although I am having greater doubts that they ever thought
about it in terms of XSLT.

Evan Lenz
XYZFind Corp.

• References:
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    • From: Kimbro Staken <kstaken@d...>

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