21. Component Based Software Development

What is a Component ?
A component was seen as an element of a software system that could be accessed, using a remote procedure call mechanism, by other components running on separate computers. Components are higher-level abstractions than objects and are defined by their interfaces. They are usually larger than individual objects and all implementation details are hidden from other components

What is CBSE ?
CBSE is the process of defining, implementing, and integrating or composing loosely coupled, independent components into systems.

Benefit of CBSE
It has become as an important software development approach because software systems are becoming larger and more complex. Customers are demanding more dependable software that is delivered and deployed more quickly. The only way that we can cope with complexity and deliver better software more quickly is to reuse rather than reimplement software components

Design Principles of Components
1. Components are independent so they do not interfere with each other’s operation. Implementation details are hidden. The component’s implementation can be changed without affecting the rest of the system.
2. Components communicate through well-defined interfaces. If these interfaces are maintained, one component can be replaced by another, which provides additional or enhanced functionality.
3. Component infrastructures offer a range of standard services that can be used in application systems. This reduces the amount of new code that has to be developed

Essential Requirements for CBSE
1. Independent components that are completely specified by their interfaces. There should be a clear separation between the component interface and its implementation. This means that one implementation of a component can be replaced by another, without changing other parts of the system.
2. Component standards that facilitate the integration of components. These standards are embodied in a component model. They define, at the very minimum, how component interfaces should be specified and how components communicate. Some models go much further and define interfaces that should be implemented by all conformant components. If components conform to standards, then their operation is independent of their programming language. Components written in different languages can be integrated into the same system.
3. Middleware that provides software support for component integration. To make independent, distributed components work together, you need middleware support that handles component communications. Middleware for component support handles low-level issues efficiently and allows you to focus on application-related problems. In addition, middleware for component support may provide support for resource allocation, transaction management, security, and concurrency.
4. A development process that is geared to component-based software engineering.

Problems with CBSE
CBSE is now a mainstream approach to software engineering—it is a good way to build systems. However, when used as an approach to reuse, problems include component trustworthiness, component certification, requirements compromises, and predicting the properties of components, especially when they are integrated with other components.

Stages of CBSE

1. Component qualification – it is the process of finding suitable components  and evaluating/ conducting an assessment of potential benefits and costs of chosen components  . the most suitable qualified components are then selected for further adaptation
2. Component adaptation – the selected components are modified , improved , to prepare for the next step (ie integration)
3. Component composition (integrating) – it is the process of systematically integrating the selected components
4. Component engineering (design for reuse and implementation of ‘new’ components)

How does it differ from Traditional Software Engineering ?
The process of component-based system development differs from ‘traditional’ development processes.
The main difference is in the separation of the development process of components from the development process of systems.
For the system-level process, the emphasis is on finding the proper components and verifying/evaluating and integrating them. For the component-level process, design for reuse is the main concern.
Component assessment is a new (possibly separate) process for finding and evaluating components.

Try this 
March 2017 A3 
c) Component based systems development (CBSD) methods place a lot of emphasis on component reuse, hence they differ from ‘traditional’ systems development methods.
You are asked:
(i) to briefly explain the main differences between ‘traditional’ and CBSD process/life cycle models;
(4 marks)
(ii) to discuss the main stages of CBSD methods.(7 marks)