[xsl] Ways to simplify XSL, complex "select/filter criteria"

Hi all,

first my environment: Saxon 8.9, XSL and Xpath 2.0, Java

I have to transform a XML document which contains elements with the same 
name but different xs:type.
In addition the elements contain an optional validFor element which 
defines a time period for the validity of the data.
The rules to implement is:
- select element by xsi type
- select the valid (in time period) element
- if no time period specified and multiple elements of the same type 
exist, take the first one
I have to apply these rules in almost every value-of selection in my 
XSLT and therefore the XSLT became really a nightmare.
I hope there is a solution to simplify this. I though about 
xsl:function, dynamic Xpath (saxon:evaluate,..) but couldn't get it to work.
Any help more than appreciated!

Thanks
Stefan

simplified XML and XSL:

<ns:Individual
xsi:type="ns:Individual"
xmlns:ns="http://myns";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>

<ns:validFor xsi:type="ns:TimePeriod">
<ns:startDateTime>1800-01-01T00:00:00</ns:startDateTime>
<ns:endDateTime/>
</ns:validFor>

<ns:PartyPlays xsi:type="ns:Employee">
<ns:validFor xsi:type="ns:TimePeriod">
<ns:startDateTime>2005-09-19T00:00:00</ns:startDateTime>
<ns:endDateTime/>
</ns:validFor>
<ns:PartyRoleContactableVia xsi:type="ns:PostalContact">
                ...
</ns:PartyRoleContactableVia>
<ns:PartyRoleContactableVia xsi:type="ns:PostalContact">
            ...
</ns:PartyRoleContactableVia>
<ns:PartyRoleContactableVia xsi:type="ns:EMailContact">
<ns:validFor xsi:type="ns:TimePeriod">
<ns:endDateTime>2010-09-19T00:00:00</ns:endDateTime>
</ns:validFor>
<ns:eMailAddress>email1(_at_)my(_dot_)com</ns:eMailAddress>
</ns:PartyRoleContactableVia>
<ns:PartyRoleContactableVia xsi:type="ns:EMailContact">
<ns:validFor xsi:type="ns:TimePeriod">
<ns:endDateTime>2010-09-19T00:00:00</ns:endDateTime>
</ns:validFor>
<ns:eMailAddress>email2(_at_)my(_dot_)com</ns:eMailAddress>
</ns:PartyRoleContactableVia>
</ns:PartyPlays>
</ns:Individual>


<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; xmlns:cdm="http://myns"; 
xmlns:xs="http://www.w3.org/2001/XMLSchema"; 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>
<xsl:output method="text"/>

<xsl:template match="/">
<xsl:value-of 
select="/cdm:Individual/cdm:PartyPlays[contains(@xsi:type,'Employee')][
if(string-length(cdm:validFor/cdm:startDateTime) gt 0 and 
string-length(cdm:validFor/cdm:endDateTime) gt 0) then
(xs:dateTime(cdm:validFor/cdm:startDateTime) lt current-dateTime() and 
xs:dateTime(cdm:validFor/cdm:endDateTime)gt current-dateTime())
else if(string-length(cdm:validFor/cdm:startDateTime) gt 0) then
(xs:dateTime(cdm:validFor/cdm:startDateTime) lt current-dateTime())
else if(string-length(cdm:validFor/cdm:endDateTime) gt 0) then
( xs:dateTime(cdm:validFor/cdm:endDateTime)gt current-dateTime())
else
1
]/cdm:PartyRoleContactableVia[contains(@xsi:type,'EMailContact')][
if(string-length(cdm:validFor/cdm:startDateTime) gt 0 and 
string-length(cdm:validFor/cdm:endDateTime) gt 0) then
(xs:dateTime(cdm:validFor/cdm:startDateTime) lt current-dateTime() and 
xs:dateTime(cdm:validFor/cdm:endDateTime)gt current-dateTime())
else if(string-length(cdm:validFor/cdm:startDateTime) gt 0) then
(xs:dateTime(cdm:validFor/cdm:startDateTime) lt current-dateTime())
else if(string-length(cdm:validFor/cdm:endDateTime) gt 0) then
( xs:dateTime(cdm:validFor/cdm:endDateTime)gt current-dateTime())
else
1
][1]/cdm:eMailAddress[1]"/>
</xsl:template>
</xsl:stylesheet>



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