Re: Modelling Disjoint Subtypes

Joe Thurbon wrote:

> Bob Badour wrote:
>

>> Joe Thurbon wrote:
>>
>>> Am I just barking up the wrong tree? Would you like to tell me the 
>>> answer?
>>
>> You are barking up the wrong tree. If at all possible, the only 
>> constraints one should have are foreign key references. What exactly 
>> prevents one from using a foreign key constraint to enforce the 
>> disjoint requirement?

The foreign key constraints for N-1 subtypes require N-1 foreign key constraints.

If one uses foreign key constraints to enforce disjointedness among the same subtypes, presumably one may use at least as many foreign key constraints.

> Or, more explicitly, if
> - a table COMMON contains columns that are common to a number of
> entities, and COMMON has a primary key K; and
> - tables SUBTYPE1 ... SUBTYPEN represent specialisations of COMMON,
> these tables also have a primary key K which references K as a foreign key.

Remember: K is a set of attributes.

> then,
>
> I want to ensure is that for each value of the attribute K appearing in
> COMMON, that value appears as the value for K in at most 1 of the tables
> SUBTYPE1...SUBTYPEN.
Indeed. Received on Thu Mar 22 2007 - 23:23:50 CET