I've got XML roughly like this:

<items>
	<item>
		<name>foo</name>
		<subjects>
			<subject>Science</subject>
			<subject>Politics</subject>
			<subject>History</subject>
		</subjects>
	</item>
	<item>
		<name>bar</name>
		<subjects>
			<subject>Science</subject>
			<subject>History</subject>
			<subject>Art</subject>
		</subjects>
	</item>
</items>

Where each item, as you can see, is categorised.

I'm transforming them, using parameters for inclusion and exclusion,
roughly like this:

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:param name="included" select="'Science'"/>
	<xsl:param name="excluded" select="'Politics'"/>
	<xsl:template match="//item">
		<xsl:if test="contains(subjects,$included) and
not(contains(subjects,$excluded))">
			<xsl:value-of select="name"/>
		</xsl:if>
	</xsl:template>
</xsl:stylesheet>

Which selects "bar", because its subjects match the included string and
don't match the excluded string.

So, all well and good if I only ever have one of each, but now I need to
add more. What if I might have any number of inclusions and exclusions?
Say I had a config file like this:

<config>
	<included>
		<subject>Science</subject>
		<subject>History</subject>
	</included>
	<excluded>
		<subject>Politics</subject>
	</excluded>
</config>

Allowing an arbitrary number of inclusions and exclusions, how would I
efficiently test each item?



=============================================================================
=
The information contained in this email and any attachment is confidential
and
may contain legally privileged or copyright material.   It is intended only
for
the use of the addressee(s).  If you are not the intended recipient of this
email, you are not permitted to disseminate, distribute or copy this email or
any attachments.  If you have received this message in error, please notify
the
sender immediately and delete this email from your system.  The ABC does not
represent or warrant that this transmission is secure or virus free.   Before
opening any attachment you should check for viruses.  The ABC's liability is
limited to resupplying any email and attachments
=============================================================================
=