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Commonality/Variability and Abstract Classes

Object-oriented design captures all three perspectives

Consider Figure 8-4. It shows the relationship between

  • Commonality/variability analysis

  • The conceptual, specification, and implementation perspectives

  • An abstract class, its interface, and its derived classes

Figure 8-4 The relationship between commonality/variability analysis, perspectives, and abstract classes.

As you can see in Figure 8-4, commonality analysis relates to the conceptual view of the problem domain and variability analysis relates to the implementation, that is, to specific cases.

Now, specification gives a better understanding of abstract classes

The specification perspective lies in the middle. Both commonality and variability are involved in this perspective. The specification describes how to communicate with a set of objects that are conceptually similar. Each of these objects represents a variation of the common concept. This specification becomes an abstract class or an interface at the implementation level.

In the new perspective of object-oriented design, I can now say the following:

Mapping with Abstract Classes


Abstract class ν the central binding concept

An abstract class represents the core concept that binds together all of the derivatives of the class. This core concept is what defines the commonality.

Commonality ν which abstract classes to use

The commonalities define the abstract classes I need to use.

Variations ν derivation of an abstract class

The variations identified within that commonality become derivations of the abstract classes.

Specification ν interface for abstract class

The interface for these classes corresponds to the specification level.

This simplifies the design process of the classes into a two-step procedure:

When Defining . . .

You Must Ask Yourself. . .

An abstract class (commonality)

What interface is needed to handle all of the responsibilities of this class?

Derived classes

Given this particular implementation (this variation), how can I implement it with the given specification?

The relationship between the specification perspective and the conceptual perspective is this: It identifies the interface I need to use to handle all of the cases of this concept (that is, the commonality).

The relationship between the specification perspective and the implementation perspective is this: Given this specification, how can I implement this particular case (this variation)?

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