grouping items from multiple xml documents

I'v read some suggested solutions for the grouping problem,
i.e. using the Muenchian method.

My situation is that I have a set of multiple 'target' xml
files together with a single 'master' xml file referencing
them. The 'target' files contain records, identifiable by
id. These records usually show up in multiple targets (i.e.
documents)...

I'd like to generate a matrix (html table) showing all
records for all targets, each cell containing the actual
content of the records in the various target documents.

The problem is that the Muenchian method to generate the
table rows relies on a way to identify the nodes by either
id() or key(), which doesn't work across document boundaries.
I.e. I apparently can't group nodes together that come from
different documents.

Thanks a lot,
		Stefan