>I was trying to think of how to eliminate the table.field combination, but I think this needs to be retained: one might also need to identify the originating database, so to generalise (using 'handle' to indicate some combination of table/field-name, etc.:

Actually, this way you can keep everything in just two tables: trail and entities. The entitites table would play the role of the dbc, i.e. contain all the rules and containterships. There you could have fields, tables, tables of tables etc, with unlimited hierarchy and not limited even to a strict tree - it could be more banyan-like, if need be; one field may belong to more than one table. Hm, don't know how that one would work, the logic may be quirky.

Anyway, your handle, as in

>datetimeStamp/handle/value/virtualPK/User

would point to a record in the entities table. And that would be all.