With a posting titled
XQuery -- Reinventing the Wheel?, Evan Lenz has sparked
a
discussion on xml-dev regarding what he
describes as a "tremendous amount of overlap in the
functionality provided by XQuery... and that provided by
XSLT".
Lenz's implication is that the functionality overlap in
XQuery is unnecessary:
...the overlap between XQuery and XSLT is far too
great for the W3C to reasonably recommend them both as
separate languages. If XSLT (or XSLT 2.0) isn't considered
adequate as an XML query language by itself, then the
development of an XML query language should still build
from the same semantic and syntactic base as XSLT
He goes on to provide a simple formula describing what he
sees to be the relationship between the two languages:
XQuery = XSLT - templateRules - nonAbbreviatedXPathAxes
And he elaborates in a
paper
which he indicates is adapted from a presentation he will
give at the upcoming
XSLT-UK conference.
In a
response that's worth reading in full, Jonathan Robie
(one of the editors of the XQuery Working Draft,
as well as several related documents)
begins by pointing out that the list of XQuery editors includes
"a former member of the XSL Working Group,... one of the
inventors of SQL, one of the inventors of XML-QL, and one of
the inventors of XQL, a precursor of XPath." He goes on to
explain:
XQuery and XSLT will share a common expression
language, including path expressions. XSLT is really two
languages, an XML-based language used to write the
templates, and XPath, an expression language used for
patterns. Both XQuery and XSLT will use XPath 2.0, and the
two Working Groups are working closely together on this. So
the two languages will share a great deal.
That said, he gives three areas that he believes to justify
creating XQuery as a language separate from XSLT:
-
ease of use
-
optimizability
-
strong data typing
And he goes on to provide details about each area.
The XQuery debate follows an earlier, more general
discussion and
followup on xml-dev (kicked off by a posting,
titled
intertwined specs, from Simon St.Laurent) regarding
movement "toward a jungle of intertwined specs, with
complexity increasing despite/because of reuse".
That earlier discussion is summarized and elucidated by
Leigh Dodds in his February 21st XML-Deviant
column.
(Dodds and St.Laurent are both xmlhack contributing
editors.)
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