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Re: [xsl] My first attempt at XSLT streaming -- it works! But why?


Subject: Re: [xsl] My first attempt at XSLT streaming -- it works! But why?
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Wed, 21 Aug 2013 21:23:22 +0100

The statement "These examples no longer work" was left over from a draft in
which the examples didn't work; we fixed the examples to use xsl:iterate as
suggested in the note, but failed to remove the note.

In fact, in the latest draft the original versions of these examples (using
count() in this case) are now streamable again.

However, do note that Saxon's streaming implementation will stream some things
that are not streamable according to the W3C spec, and vice versa. This is
very much work in progress.

Michael Kay
Saxonica


On 21 Aug 2013, at 20:47, Costello, Roger L. wrote:

> Hi Folks,
>
> I have an XML document that contains a bunch of <Book> elements. I want my
XSLT program to use streaming to count the number of Books. I mimicked the
example in the XSLT spec, section 19.1.1 (Examples of xsl:stream).
>
> My XSLT program produced the correct result. Yea! But then I read this at
the top of section 19.1.1 in the XSLT spec:
>
> 	These examples no longer work; it is no longer
> 	possible to compute an aggregate over descendant
> 	values using a path expression. Instead, traversal
> 	using templates is required.
>
> Hmm, apparently my XSLT program should not have worked. So why did it work?
>
> What is the "right" way to write the streaming code?
>
> I am using oXygen XML, which uses Saxon 9.5.0.2
>
> Here is my XSLT program:
>
> ---------------------------------------------------------
> <?xml version="1.0" encoding="UTF-8"?>
> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>                xmlns:xs="http://www.w3.org/2001/XMLSchema"
>                exclude-result-prefixes="#all"
>                version="3.0">
>
>    <xsl:output method="xml" />
>
>    <xsl:template match="/">
>        <xsl:stream href="BookCatalogue.xml">
>            <count>
>                <xsl:for-each select="BookCatalogue">
>                    <xsl:iterate select="Book">
>                        <xsl:param name="count" select="0" as="xs:decimal"/>
>                        <xsl:next-iteration>
>                            <xsl:with-param name="count" select="$count+1"/>
>                        </xsl:next-iteration>
>                        <xsl:on-completion>
>                            <xsl:value-of select="$count"/>
>                        </xsl:on-completion>
>                    </xsl:iterate>
>                </xsl:for-each>
>            </count>
>        </xsl:stream>
>    </xsl:template>
>
> </xsl:stylesheet>
> ---------------------------------------------------------
>
> And here is my XML document:
>
> ---------------------------------------------------------
> <?xml version="1.0"?>
> <?xml-stylesheet type="text/xsl" href="BookCatalogue.xsl"?>
> <BookCatalogue>
>        <Book>
>                <Title>Six Great Ideas</Title>
>                <Author>Mortimer J. Adler</Author>
>                <Date>1981</Date>
>                <ISBN>0-02-072020-3</ISBN>
>                <Publisher>Macmillan Publishing Company</Publisher>
>        </Book>
>        <Book>
>                <Title>Illusions</Title>
>                <Author>Richard Bach</Author>
>                <Date>1977</Date>
>                <ISBN>0-440-34319-4</ISBN>
>                <Publisher>Dell Publishing Co.</Publisher>
>        </Book>
>        <Book>
>                <Title>The First and Last Freedom</Title>
>                <Author>J. Krishnamurti</Author>
>                <Date>1954</Date>
>                <ISBN>0-06-064831-7</ISBN>
>                <Publisher>Harper &amp; Row</Publisher>
>        </Book>
> </BookCatalogue>
> ---------------------------------------------------------


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