>Nadya,
>
>FK constraints on lookups are every bit as critical. If you use a single overloaded lookup table you need to ensure that you constrain the lookuptype for a given FK into the lookup.
>
>>In this question I was more concerned about lookup tables. Of course, for real parent and child we must have triggers in place. I do agree with having them for lookup as well, but want to find out the general practice.

That was originally implemented with very fanky indexes. We changed the indexes, but left the constrains. So, you're right, they don't make much sense now!

Thanks for helping me in realizing that.