[xsl] Comparing attribute values of nodes in different contexts

Consider the following XML document, showing a set of telephone calls
received from a specific telephone number, along with the various
internal connections to different employees from the time the call is
first connected to the phone system until the call is terminated.


<caller callerID="9195551212">
    <contact
        callID="1"
        contactID="3"
        timeCallInitiated="2010-02-04T09:42:58"
        timeAgentConnected="2010-02-04T09:43:23"
        agent="Jamie Smith"
    />
    <contact
        callID="1"
        contactID="2"
        timeCallInitiated="2010-02-04T09:42:58"
        timeAgentConnected="2010-02-04T09:43:23"
        agent="Angela Jones"
    />
    <contact
        callID="1"
        contactID="1"
        timeCallInitiated="2010-02-04T09:42:58"
        timeAgentConnected="2010-02-04T09:42:58"
        agent="Desi Johnson"
    />
    <contact
        callID="2"
        contactID="3"
        timeCallInitiated="2010-02-04T09:41:45"
        timeAgentConnected="2010-02-04T09:42:10"
        agent="Jamie Smith"
    />
    <contact
        callID="2"
        contactID="2"
        timeCallInitiated="2010-02-04T09:41:45"
        timeAgentConnected="2010-02-04T09:42:10"
        agent="Angela Jones"
    />
    <contact
        callID="2"
        contactID="1"
        timeCallInitiated="2010-02-04T09:41:45"
        timeAgentConnected="2010-02-04T09:41:45"
        agent="Julia Billings"
    />
    <contact
        callID="3"
        contactID="2"
        timeCallInitiated="2010-01-26T13:29:21"
        timeAgentConnected="2010-01-26T13:29:49"
        agent="Angela Jones"
    />
    <contact
        callID="3"
        contactID="1"
        timeCallInitiated="2010-01-26T13:29:21"
        timeAgentConnected="2010-01-26T13:29:21"
        agent="Desi Johnson"
    />
</caller>

Ideally this XML file would be one level deeper where all "contacts"
having the same value for the callID attribute are grouped together
under a single node. I cannot change that however. And therein lies my
problem. To dumb this down I'd like output as follows:

        Call Connected on 2010-02-04
        There are 3 related connections as follows:
        Connection: 2010-02-04T09:43:23 to agent Jamie Smith
        Connection: 2010-02-04T09:43:23 to agent Angela Jones
        Connection: 2010-02-04T09:42:58 to agent Desi Johnson
        Call Connected on 2010-02-04
        There are 3 related connections as follows:
        Connection: 2010-02-04T09:42:10 to agent Jamie Smith
        Connection: 2010-02-04T09:42:10 to agent Angela Jones
        Connection: 2010-02-04T09:41:45 to agent Julia Billings
        Call Connected on 2010-01-26
        There are 2 related connections as follows:
        Connection: 2010-01-26T13:29:49 to agent Angela Jones
        Connection: 2010-01-26T13:29:21 to agent Desi Johnson

The Key problem is just one little piece of this:
        'There are 3 related connections as follows:'
How do I get the '3' computed?

For my application, it is important that I output that number BEFORE I
output each of the connections.
Here's the code to produce that output above (with one incomplete part):

        <xsl:template match="/caller">
          <xsl:for-each select="contact">
            <xsl:if test="not(@callID = preceding-sibling::contact[1]/@callID)">
                <br/>
                Call connected on <xsl:value-of
select="scripts:justDate(@timeCallInitiated)"/>
                <br/>
                There are
                <xsl:value-of select="count(/caller/contact[(_at_)callID = 
?])"/>
                related connections as follows:
            </xsl:if>

            <br/>
            Connection:
                <xsl:value-of select="@timeAgentConnected"/>
            to agent
                <xsl:value-of select="@agent"/>
          </xsl:for-each>
        </xsl:template>

See that question mark '?' up there? What goes there? The @callID
refers to the context of the preceding XPath expression. I want to
only count those 'contact' nodes that have the same attribute value of
'callID' as the node being currently processed by the for-each node.
But I have no idea how to reference the context of the for-each node
from within that count function.

I clearly need a better theoretical understanding of how different
contexts are used in the XSL processing. But there seems to be a large
gap between the technical documentation at w3c and how to even ASK
about problems like this!

Any help here?

A totally alternative approach to the XSL stylesheet is perfectly acceptable.

Best

Robert H. Bourdeau

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