perl D:\scheduler\XMLProcessing.pl "D:\scheduler\DSMapped\onlineRateReporting.xml#child::reportLine[{declare Join(@Key) match href(runtimes.xml#attribute::Key(@Join)[{declare RunTime(@Time)}]) replace Scheduled(@RunTime)}]"

where Perl executes the application XMLProcessing.pl with the argument between double-quotes. This is the XPath command, extended to use predicate-processing ( between {}). The meaning is: take onlineRateReporting.xml child nodes called reportLine, declare a variable 'Join' with the value of those nodes 'Key' element, match those values against runtimes.xml attributes called 'Key' values, and if match declare a variable 'RunTime' with the value of 'Time' element and use this to update element 'Scheduled' in the first xml file.

This may not be exactly what you are looking for.

Best Regards

Julius