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Friday, November 30, 2007

XProc: An XML Pipeline Language

W3C has announced the release of a new version of the Working Draft for
"XProc: An XML Pipeline Language." This document was produced by the
XML Processing Model Working Group which is part of the XML Activity.
In response to comments made on the previous draft, the Working Group
decided to make significant changes to the way XPath and XSLT are
supported in XProc. In particular, the requirement to support XPath 1.0
as XProc's expression language has been relaxed and the two XSLT steps
have been combined into a single step. The Working Group has not finished
addressing all of the outstanding comments on its previous draft but
feels that the XPath change in particular has such a pervasive impact
on the language that it has decided to publish a new draft immediately
in order to expose this decision. User and implementor feedback on this
decision would be most valuable. Norm Walsh writes in his blog
commentary: "The decision to wrap both versions of XSLT up into a
single step makes the signature for the step a little odd in the XSLT
1.0 case, but workable. Pipeline authors can choose the version they
want, implementors can choose the version automagically if authors don't.
Implicit pipeline inputs and outputs were designed to make very simple,
straight through pipelines as short as possible (syntactically). But
they added significant complexity to the analysis of pipelines that
call pipelines. So now we require all the inputs and outputs of a
'p:pipeline' [element] to be explicit." XProc defines a language for
describing operations to be performed on XML documents. An XML Pipeline
specifies a sequence of operations to be performed on one or more XML
documents. Pipelines generally accept one or more XML documents as input
and produce one or more XML documents as output. Pipelines are made up
of simple steps which perform atomic operations on XML documents and
constructs similar to conditionals, loops and exception handlers which
control which steps are executed. More Information See also the blog by Norm Walsh: Click Here

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