Test if an element with a certain value exists

[bdbull]

I've come across a problem that seem simple, but I can't figure out
how to do this. I need to capture a value while processing a file,
then check if that value exists in another file. I'm able to capture
the value, but it's the other part that I'm hanging up on. For
example, say I capture the value 'charles' and I want to see if it
exists in the below xml:

external.xml
-------------------
<class>
<student>bob</student>
<student>mary</student>
<student>charles</student>
<student>roy</student>
</class>

I know I need to use the document() function to pull in the external
xml file, but I'm not sure how I test for the existence of an element
whose value is X.

Any help?

[bdbull]

If need be, I can change the format of the external xml file to be
like the following:

external.xml
-----------------
<class>
<student name="bob"/>
<student name="mary"/>
<student name="charles"/>
<student name="roy"/>
<class>

I just can't seem to figure this out.

[Mukul Gandhi]

you don't need to change the structure of external.xml.

for the previously posted external.xml, following will be the solution
for this,

Let's say you have already got some value in a XSLT variable, x
(xsl:variable name="x" ...).

The XSLT code for this problem will be,

<xsl:variable name="external" select="document('external.xml')" />

<xsl:if test="$external/class/student = $x">
... do something
</xsl:if>

Cheers,
Mukul