August 2013 Archive


Types in ODL

ODL gives the database designer a type system similar to that found in C or other usual programming languages. A type system is built from a basis of types that are described by themselves and certain recursive rules whereby complicated types are built from simpler types. In

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.

Extents

When an ODL class is part of the database being described, we need to differentiate the class definition itself from the set of objects of that class that exist at a given time. The difference is the same as that between a relation schema and a relation instance, even though both can

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