A Super-sub relation is one in which the sub-entity is considered to be "a kind of" or "a part of" the super entity. The primary key of the super entity is always the primary key of the sub-entity; in a logical data model, the sub-entity usually has one or more attributes that are not in the super entity, and not in any other sub-entity of the super entity.

When you create a Physical Data Model from the ERD, you are given the choice of migrating the attributes of the sub-entity to the table created from the super entity; migrating the attributes of the super to the sub; or creating separate tables for each. There is no "right answer"; every system has its own reasons for determining which approach makes more sense.