Question

I am refactoring an xslt for word xml to improve performance as recommended here. I am relatively new to xslt. Why are the following statements not equivalent?

Form1

<xsl:value-of select="//w:style[@w:styleId = $styleName][ancestor::pkg:part/@pkg:name='/word/styles.xml']"/> 

Form2

<xsl:value-of select="/pkg:package/pkg:part[@pkg:name='/word/styles.xml']/child::w:style[@w:styleId = $styleName]" />

Note that pkg:package is the root and pkg:part are direct children.

Form1 states that get the w:style element with the attribute equaling $styleName, whose ancestors are pkg:part with attribute @pkg:name='/word/styles.xml'.

Form 2 states that get the w:style elements with the attributes equaling $styleName who are children of pkg:package/pkg:par@pkg:name='/word/styles.xml'

The actual statement I am trying to rewrite is this one:

<xsl:value-of select="//w:style[@w:styleId = $styleName][ancestor::pkg:part/@pkg:name='/word/styles.xml']/w:pPr/w:numPr/w:numId/@w:val"/>

Thank you.

Answer 1

Your second XPath is on the right track, but it would only match w:styles that are direct children of pkg:part (the child:: axis is redundant here), which I don’t think they are. This should work:

/pkg:package/pkg:part[@pkg:name='/word/styles.xml']//w:style[@w:styleId = $styleName]

and I think this is an improvement over the original XPath, but it still has a // in it. My knowledge of wordprocessingML is not very extensive, but is it the case that all <w:style>s are the children of <w:styles> elements, which are all children of a <pkg:xmlData> element? If so, this should work (split across 2 lines for readability):

/pkg:package/pkg:part[@pkg:name='/word/styles.xml']
                               /pkg:xmlData/w:styles/w:style[@w:styleId = $styleName]

One other possibility for improving performance is to use a key. In your XSLT, you would define a key like this:

<xsl:key name="kStyle" match="w:style" use="@w:styleId" />

And then you would access the style you want like this:

<xsl:value-of select="key('kStyle', $styleName)
                               [ancestor::pkg:part/@pkg:name = '/word/styles.xml']
                               /w:pPr/w:numPr/w:numId/@w:val" />

Key lookups are generally very efficient, so this second option may be the better one in terms of performance.