Dave: I thought about adding a table to store the directed links and a second table to store the full closure of the directed graph (store for all categories the categories that automatically result from choosing them; start with self-references). When inserting a categorization for an object i'll join with this full-closure table and insert the result set.
Some questions remain: Should there be a way of turning off these linked categories? Probably for every object-tree mapping? Should we also give the option of just turning off linked categories in trees not mapped to an object? Or should there be a finegrained way of turning off some links?
