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[xsl] Does use a lot of memory? Is there an alternative that is more efficient?


Subject: [xsl] Does <xsl:copy> use a lot of memory? Is there an alternative that is more efficient?
From: "Costello, Roger L." <costello@xxxxxxxxx>
Date: Sun, 2 Sep 2012 12:47:38 +0000

Hi Folks,

Does <xsl:copy> use a lot of memory?

Is there an alternative that is more efficient?

Consider this problem. I have an XML document in which some elements have an
id attribute and others have an idref attribute. If an element A references
element B, then I want to embed B inside A.

Example: I want to convert this:

<Test>
    <A idref="b" />
    <B id="b" />
</Test>

to this:

<Test>
    <A>
        <B id="b" />
    </A>
    <B id="b" />
</Test>

Notice that A references B, and after processing B is nested inside A.

Here's a template that handles elements with a reference:

    <xsl:key name="ids" match="*[@id]" use="@id"/>

    <xsl:template match="*[@idref]">

        <xsl:variable name="refed-element" select="key('ids', @idref)"/>

        <xsl:copy>
            <xsl:copy-of select="@* except @idref" />
            <xsl:sequence select="$refed-element" />
        </xsl:copy>

    </xsl:template>

The complete program is below.

It works fine if:

(a) The XML document is small.
(b) I don't have to repeat this embedding process too many times.

However, such is not the case. I am dealing with an XML document that is 370
MB in size and has tens of thousands of references. And I have to repeat the
embedding process multiple times.

Saxon gives me an "out of memory error."

I suspect the reason for this is due to the <xsl:copy> command. I believe it
is making new copies, thereby consuming lots of memory. True?

So, is there an alternative to <xsl:copy> that is more efficient?

Is there a way to express the above template rule that is more efficient?

/Roger
-----------------------------------------------------------------------------
------------
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                exclude-result-prefixes="#all"
                version="2.0">

    <xsl:output method="xml" />

    <xsl:key name="ids" match="*[@id]" use="@id"/>

    <xsl:template match="*[@idref]">

        <xsl:variable name="refed-element" select="key('ids', @idref)"/>

        <xsl:copy>
            <xsl:copy-of select="@* except @idref" />
            <xsl:sequence select="$refed-element" />
        </xsl:copy>

    </xsl:template>


    <xsl:template match="node()">

        <xsl:copy>
            <xsl:copy-of select="@*"/>
            <xsl:apply-templates />
        </xsl:copy>

    </xsl:template>

</xsl:stylesheet>


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