Implement a Map created from docA, used to transform d

One input document is processed to create what is (in Java terms) a
Map<String,String>.
To transform another document, lookup of map keys for values needs to be done
repeatedly and frequently.

Each key is composed from values scattered all over the 1st document;
I think that
I'll have to use functions to collect the chunks, which may iterate
over sequences
and call other functions, and so, finally, down in one such function,
I'll have a key
and its value.

I think that a third (internal only) document with a flat structure containing
multiple <e><k/><v/></e> is the best (the only?) way of implementing this map.

Any comments welcome - I hope this isn't too abstract.
-W