Re: Separate foreign keys with shared ID space

Your design may need some more consideration.

From a theoreticaly relational design standpoint, when you have a entity type that has subtypes, at the ERD stage, you have to figure out the attributes that belong to the (supertype), attributes that belong to each subtype, and optionality of each of those attributes.

When you are ready to consider creating tables from those entities ... you have a choice.

You can either create one table the supertype and in that table it will have all of the columns that belong to the supertype plus all of the columns that belong TO EACH of the subtypes.

OR

You do not create the supertype table and then you create a separate set of tables for each subtype. In each subtype go all of the columns from the supertype along with the specific set of columns that belong to the subtype.

Then there are programming tradeoff's that depend on which way the design tradeoff was implemented.

It appears to me if I understand what you presented, you have both the supertype table along with the subtype tables. That looks wrong to me. Received on Wed Jul 28 2004 - 10:21:19 CDT