hello db gurus! :-)
got a problem, that i cannot solve for three days already

1. there are 2 types of owners (person and factory)

2. owner can be only a person or factory (xor in other words)

3. owner has many relationships with other entities (for note)

4. person can be a doctor, specialist and so on with the corresponding properties

so the question is how to implement this into db design.. which tables to create

my idea was

owner(pk: owner_id)
person(pk: person_id, fk: owner_id)
factory(pk: factory_id, fk: owner_id)

the BUG is that first i MUST create record in table owner and then copy it into person or factory table depending on owner type with that all owner_id MUST unque.

to place factory and person into one table is not very good design i guess

if to divide them into 2 tables

person(pk: owner_id)
factory(pk: owner_id)

then i have to find a way to keep owner_id unique

what i should do? help me please

reading over your post a few times, i was having trouble understanding where the problem is, until it suddenly struck me -- you're thinking of using an autonumber/identity type primary key, right?

you're right, combining person and factory is probably not a good idea

just go with your initial design, however, with a small change --

owner(pk: owner_id)
person(pk/fk: owner_id)
factory(pk/fk: owner_id)

yes, you still must first create the owner row, then use the autonumber/identity key value to create the related row in either person or factory

that's not a problem, that's a feature

but in those tables, it is not an autonumber/identity

brilliant! thanks a lot!