DataMap is a class structure that maps a single key to multiple values.

I'm supposed to design a class structure called JoinMap which keeps a pair of keys of two DataMaps.

As far as I understood, a JoinMap is meant to join data from two DataMaps into a single view. It somehow reminds of the CompositeMap class structure available in the Jakarta Apache Commons Collections.

Any idea how I should implement this ? Does anyone how a CompositeMap actually works?