[xsl] Updating xml - difference between MSXML and Xalan

["Pete & Angie Taylor" <pandatay@xxxxxxxxxxxxx>]

Dear List,

We have a working document that can get large (100kb + ) and is frequently
updated by being transformed and then completely replaced by the
transformation result - a sort of xslt master file update.

I am trying to improve performance by only transforming the nodes that need
to change, avoiding the high cost of repeatedly copying the 90% plus that
does not change each time.

The basic idea is for my application code to identify one or more templates
that handle the changes (name startswith "replace"), find all nodes that are
matched by any of these templates, transform each node, and replace each
node with the result of its transformation. (I.e. to do a number of very
small translations of particular nodes, rather than one very large
translation of the whole document.)

For example, if my working document looks like this -

<a>
    <b>before</b>
</a>

and I have a stylesheet with an identity template and a template like this -

<xsl:template name="replace1" match="/a/b">
    <xsl:copy>after</xsl:copy>
</xsl:template>

then my application finds the template named "replace1", finds the node that
is matched by "/a/b" and transforms and replaces just that node. The result
is -

<a>
    <b>after</b>
</a>

When I transform the non-root <b> node rather than the whole document, MSXML
matches it with the "replace1" template, and I get the result I expect. I
can demonstrate a huge saving when repeatedly making small updates to a
large document.

But when I try to transform the <b> node in Xalan (transformer.transform(new
DomSource(node)) ) it fails to match my <b> node with the path "/a/b". I can
only get my <b> node to be matched by a template with a match attribute of
exactly "b".

My question is: if I transform a node other than the root node of an xml
document using xslt, should the node be matched by a template which has a
match starting from the root? (Should my <b> node be matched by my "/a/b"
template?) Any idea why Xalan doesn't seem to do it? Is it me? (It usually
is!)

Thanks in advance - and thanks for many many interesting posts in the past.

Pete Taylor