data-modeling question

Hello guys, After i perform generalization, i have come-up with a data model where Super-Sub relationship exist. However some of the sub-types are so similar to extand that all of its attributes are in Super-type entity. But i still need to differentciate between those sub-types, as such i created sub-types with only one attribute that is the primary key of super-type. Example. of this is as follow, Entity Name Entity type Entity Attributes Person Super ID, Name, Address, Phone, Sex, Marital-Status, Birth-Day. Employee Sub ID Customer Sub ID, c-attrib1, c-attrib-2. Supplier Sub ID, s-attrib1, s-attrib-2. The rules are, an Employee can also be a customer, a supplier can also be a customer, but a supplier cannot be an Employee and vice versa. The relationship between super and sub is a ISA relationship. The reason i use ID as a primary key is to narrow down the search path, and time taken to retrieve the record as well as to reduce complexity of unnecessary validation and also to follow the integrity rules and reduce redundancy. Previously that is before genaralization, there exist 3 separate tables with all the similar attributes. Finaly the table Employee only left with ID attribute. Here i would like to seek advice, should this table exist? how can i find out if a customer is an employee? should i include another attributes in the person table to define this? Syed ---------- Signature ----------- Name: Syed Ibrahim Address: Sapura Advanced Systems Sdn. Bhd, 18th Floor, Menara Tun Razak, Jalan Raja Laut, 50350 Kuala Lumpur, Malaysia Tel: (03) 295-3472, (03) 294-3000 Fax: (03) 294-6587, (03) 293-3154