Use case driven approach is a method of object oriented software engineering (OOSE) developed by Jacobson et al (1992). The requirement model of the use case driven approach software system is defined by a collection of use cases, problem domain descriptions and user interfaces. Extension is an important type of association between use cases. Extension means that a use case that represents the major or basic course of events can be naturally extended with one or several other use cases that represent rare or exceptional courses of events. A difficulty for OOSE to transform the use cases with extension associations into the design and implementation model of the system is that most programming Languages, such as C++, Smalltalk and Java, do not have features to support the extension association. The current implementation of an extension association still relies on the basic course use case to initiate the extension use cases.;This thesis presents a programming technique to overcome the difficulty described above. It supports the integration of a major course use case and its extension use cases. Based on this technique, a mechanism extension construct invocation is proposed to directly support the extension association between use cases. The extension statement and probing clause allow an extension use case to automatically respond to any extension request from a basic course use case. This mechanism reduces the responsibility of a method that represents a basic course use case with extension statements. The probing clause added to a method that represents an extension use case can automatically respond to any extension request from a basic course use case.
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