Basic Database design question - 1 attribute three Entities

Question

Hello.

Please can someone clarify something which I should really know by now?

If I have Three Entitys Organisation, Director and Company secretary and each have the attribute primary address.

If I were modelling a conceptual ERD should I have the attribute ‘primary address’ separately in each entity or should I model a fourth entity Address, add primary address and have them all PK > FK to that?

Have since found this link http://stackoverflow.com/questions/307027 which pretty much covers everything I need to know.

Answer 1

I would do something like this, assuming primary address refers to the Organization location:

Table: Organization

Org_Key {PK},
Org_Name,
Primary Address fields,
Any other fields

Table: Personnel

Person_Key {PK},
Org_Key {FK},
Position {Directory, secretary, etc},
Any other fields

In my opinion, there is really no need to separate those who are "Directors" from those who are "secretaries" because they are both employees of a specific Organization.

Now, if by primary address you mean a personal address (i.e., an individuals home address) then I would add additional fields to the Personnel table.