Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe
Slide 7- 30
Mapping EER Model Constructs to
Step 9: Mapping of Union Types (Categories).
For mapping a category whose defining
superclass have different keys, it is customary to
specify a new key attribute, called a surrogate key,
when creating a relation to correspond to the
In the example below we can create a relation
OWNER to correspond to the OWNER category
and include any attributes of the category in this
relation. The primary key of the OWNER relation is
the surrogate key, which we called OwnerId.