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Friday, February 18, 2011

Component Level Design - Designing Class based Components - Cohesion

Cohesion in context with component level design refers that a component or class encapsulates only attributes and operations that are closely related to each other and to the class or component itself.


It is exhibited mainly by operations. This type of cohesion occurs when a module performs one and only one computation and then returns a result.
It is exhibited by packages, components, and classes. This type of cohesion occurs when a higher layer accesses the services of a lower layer, but lower layers do not access higher layers.
Operations that are performed to reflect a specific behavior or state.
Components and operations are grouped together. It allows one to be invoked immediately after preceding one was invoked. It is done even if there is no data is passed between them.
Operation on same data are defined in one class. Classes and components that exhibit functional, layer, and communicational cohesion are easy to implement, test and maintain.
Components and operations are grouped in such a manner that the first one provides input to the second one and so on.
Components, classes, or operations exist in the same category but are otherwise unrelated are grouped together. This type is less used.

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