DWH_File is used in a similar manner to NDBM_File, DB_File etc. In fact it
depends on one of these. DWH_File expands the functionality to save not
only the hash that is tied but also all the data that this hash contains
references to - that is it'll save all you list of lists and list of hashes
and so forth. And what's more, it will save objects as well - if they'll
comply with some very simple rules which don't impose any limitations to
their functionality or structure except that they can't themselves be tied
to anyone else. See the "Models" section of the embedded documentation for
details.