Subject: Re: [xsl] Dynamic pipelining in XSLT 2.0 w/ Saxon extensions From: "Dimitre Novatchev" <dnovatchev@xxxxxxxxx> Date: Tue, 19 Jun 2007 05:25:40 -0700 |
Why not simply use FXSL and its support for the composition of a given list of functions?
Once we have an implementation of a library of XSLT functions, one would simply use the compiled version of FXSL or whatever else. Then no need for caching/re-compilation would exist.
We need only to conserve memory used with the document() or like functions, but hopefully the underlying garbage collector will do this job.
As for new extension functions, right now I see just two of them that are really important:
memo-apply(pFun, pArg1,...,pArgN) -- this is sufficient to make any FXSL function a memo-function -- just pass it as the first parameter to memo-apply()
cc-link(pFun, pArg1,...,pArgN) -- this would implement continuation-passing style efficiently (something similar can be done with FXSL, but I am not sure it will be efficient)
-- Cheers, Dimitre Novatchev --------------------------------------- Truly great madness cannot be achieved without significant intelligence. --------------------------------------- To invent, you need a good imagination and a pile of junk ------------------------------------- You've achieved success in your field when you don't know whether what you're doing is work or play
Hi,
One of the niftier extensions available in the Saxon library is one that allows a stylesheet to be compiled and applied dynamically.
As its designer undoubtedly anticipated, it can even provide the basis for at least a lightweight pipelining infrastructure. The stylesheet below allows the specification of a set of stylesheets to be run in sequence over the input. Presently the stylesheets are named in a top-level variable, though of course this spec could also be external (and more fully-featured). Given the variable
<xsl:variable name="processes"> <m:path>stylesheets/</m:path> <m:step>one.xsl</m:step> <m:step>two.xsl</m:step> <m:step>three.xsl</m:step> <m:done/> </xsl:variable>
the stylesheets "stylesheets/one.xsl", "stylesheets/two.xsl" and "stylesheets/three.xsl" (relative to the pipelining stylesheet) are run in series over the input document, until either a "done" element is encountered, or there are no more steps. (The "path" element may be omitted; if used it must currently appear first.)
My questions:
* This runs (tested under the current Saxon 8.9), but how will it scale? In particular, Mike Kay may be able to say whether compiled stylesheets are be cached when this is run over a set of documents. If not, wouldn't compiling each stylesheet anew for each input document be an impediment?
* Are there any obvious pitfalls or problems with this approach? (Or any not so obvious?) How does it compare to other methods?
(So far I can say only that it's really easy to use, but again I'm not sure it will scale as well as other methods. It does have the advantage, it appears, of avoiding serialization altogether until the last step.)
The stylesheet:
<?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:saxon="http://saxon.sf.net/" xmlns:m="http://mulberrytech.com/local/xslt" version="2.0" extension-element-prefixes="saxon" exclude-result-prefixes="m">
<xsl:output method="xml"/>
<!-- Saxon pipelining stylesheet:
Takes document input and passes it through a chain of transformations
The steps will run in order until a "done" element is encountered or they run out
-->
<xsl:variable name="processes"> <m:path>./</m:path> <m:step>one.xsl</m:step> <m:step>two.xsl</m:step> <m:step>three.xsl</m:step> <m:done/> </xsl:variable>
<xsl:template match="/"> <xsl:apply-templates select="$processes/m:step[1]"> <xsl:with-param name="in" select="/"/> </xsl:apply-templates> </xsl:template>
<xsl:template match="m:step"> <xsl:param name="in"/> <xsl:param name="stylesheet" select="concat($processes/m:path,.)"/> <xsl:variable name="out"> <xsl:variable name="process" select="saxon:compile-stylesheet(doc($stylesheet))"/> <xsl:apply-templates select="saxon:transform($process,$in)" mode="annotate"> <!-- 'annotate' mode will provide the result with local annotations --> <xsl:with-param name="stylesheet" select="$stylesheet"/> </xsl:apply-templates> <!-- If you don't want the result annotated, simply use <xsl:copy-of select="saxon:transform($process,$in)"/> --> </xsl:variable> <xsl:if test="empty(following-sibling::*[1])"> <xsl:copy-of select="$in"/> </xsl:if> <xsl:apply-templates select="following-sibling::*[1]"> <xsl:with-param name="in" select="$out"/> </xsl:apply-templates> </xsl:template>
<xsl:template match="m:done"> <xsl:param name="in"/> <xsl:copy-of select="$in"/> </xsl:template>
<xsl:template match="/" mode="annotate"> <xsl:param name="stylesheet" select="'not given'"/> <xsl:comment> <!-- adding a comment to the top of the result --> <xsl:text> process run: </xsl:text> <xsl:value-of select="$stylesheet"/> </xsl:comment> <xsl:text>
</xsl:text> <xsl:copy-of select="node()"/> </xsl:template>
</xsl:stylesheet>
For testing, my one.xsl, two.xsl and three.xsl stylesheets all look like this (with adjustments):
<?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="*"> <xsl:element name="{local-name()}-one"> <xsl:copy-of select="@*"/> <xsl:apply-templates/> </xsl:element> </xsl:template>
<xsl:template match="comment() | processing-instruction()"> <xsl:copy-of select="."/> </xsl:template>
</xsl:stylesheet>
Comments welcome, Wendell
====================================================================== Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx Mulberry Technologies, Inc. http://www.mulberrytech.com 17 West Jefferson Street Direct Phone: 301/315-9635 Suite 207 Phone: 301/315-9631 Rockville, MD 20850 Fax: 301/315-8285 ---------------------------------------------------------------------- Mulberry Technologies: A Consultancy Specializing in SGML and XML ======================================================================
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