This class is a faster alternative to DbRAMRelationN for relations that may
become big, but in counterpart it does not preserve the order of elements,
so it cannot be used for lists whose order is controlled by the user.
This class implements a general support for relation N, that may be used
for any DBMS (not only DbRAM); so, for some DBMSs, we may prefer to use
this implementation instead of the DBMS's own collections.
This class provides a mapping between "repository" strings
(such as "tableColumns", "tablename", etc.) and Generic meta fields
(such as "m_components", "m_name", etc.).