1. A CUSTOMER can be either a COMMERCIAL CUSTOMER or a PERSONAL CUSTOMER, which both inherit characteristics from CUSTOMER.
2. A PERSONAL CUSTOMER is also a PERSON, and inherits characteristics from PERSON.
3. A COMMERCIAL CUSTOMER has a CONTACT, who is also a PERSON, and therefore inherits characteristics from both CUSTOMER and PERSON.

NOTE that the Physical Data Model can have be generated in different ways to reflect the ways in which these logical relationships can be implemented in a Database.

Barry Williams
Principal Consultant
Database Answers