It may involve accessing locally developed components

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It may involve accessing locally- developed components or services or finding these components from an external source. Component management is concerned with managing a company s reusable components, ensuring that they are properly catalogued, stored and made available for reuse. Component certification is the process of checking a component and certifying that it meets its specification. Chapter 17 Software reuse 23 Key points CBSE is a reuse-based approach to defining and implementing loosely coupled components into systems. A component is a software unit whose functionality and dependencies are completely defined by its interfaces. A component model defines a set of standards that component providers and composers should follow. The key CBSE processes are CBSE for reuse and CBSE with reuse. 24 Chapter 17 Software reuse
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12/12/2018 5 Chapter 17 Component-based software engineering Lecture 2 25 Chapter 17 Software reuse CBSE for reuse CBSE for reuse focuses on component development. Components developed for a specific application usually have to be generalised to make them reusable. A component is most likely to be reusable if it associated with a stable domain abstraction (business object). For example, in a hospital stable domain abstractions are associated with the fundamental purpose - nurses, patients, treatments, etc. 26 Chapter 17 Software reuse Component development for reuse Components for reuse may be specially constructed by generalising existing components. Component reusability Should reflect stable domain abstractions; Should hide state representation; Should be as independent as possible; Should publish exceptions through the component interface. There is a trade-off between reusability and usability The more general the interface, the greater the reusability but it is then more complex and hence less usable. 27 Chapter 17 Software reuse Changes for reusability Remove application-specific methods. Change names to make them general. Add methods to broaden coverage. Make exception handling consistent. Add a configuration interface for component adaptation. Integrate required components to reduce dependencies. 28 Chapter 17 Software reuse Exception handling Components should not handle exceptions themselves, because each application will have its own requirements for exception handling. Rather, the component should define what exceptions can arise and should publish these as part of the interface. In practice, however, there are two problems with this: Publishing all exceptions leads to bloated interfaces that are harder to understand. This may put off potential users of the component. The operation of the component may depend on local exception handling, and changing this may have serious implications for the functionality of the component.
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