Entity Sets

Additional ODL Concepts

There are many other features of ODL that we must study if we are to express in ODL the things that we can express in the E/R or relational models. In this section, we shall cover:

Subclasses in ODL / Multiple Inheritance in ODL

Let us remember the discussion of subclasses in the E/R model from "Subclasses in the E/R Model". There is a similar capability in ODL to declare one class C to be a subclass of another class D. We follow the name C in its declaration with the keyword extends and the name D.

From ODL Designs to Relational Designs

As the E/R model is meant to be converted into a model such as the relational model when we put into operation the design as an actual database, ODL was initially meant to be used as the specification language for real, object-oriented DBMS's. Nevertheless ODL, like all object-

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