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Object-Oriented Design (OOD) Methodologies

In this method we take a slightly different view of systems development from what we have examined before. In the previous section we tended to view our system from a functional or process-based viewpoint, and related this to the data structure. While this approach does produce well-designed, working systems, the current opinion among many practitioners is that the resulting systems tend to be rigid and make it difficult to respond quickly to changes in user requirements.

Unlike its two predecessors, the object-oriented approach combines data and processes (called methods) into single entities called objects. Objects usually correspond to the real things a system deals with, such as customers, suppliers, contracts, and invoices. Object-oriented models are able to thoroughly represent complex relationships and to represent data and data processing with a reliable notation, which allows an easier mix of analysis and design in a growth process. The aim of the Object-Oriented approach is to make system elements more modular, thus improving system quality and the efficiency of systems analysis and design.

In the Object-Oriented approach we tend to focus more on the behaviour of the system. The main feature we document is the Object or Class.

What is an Object?

An Object, as we have already stated, is something we hold data about. This is usually in the form of a noun, eg an apple is an object. It has attributes such as size and colour and taste.

What is a Class?

A Class is the description of a set of common objects, eg the apple would belong to the class Fruits, which all have similar group characteristics but also wide differences between them: ie another object, Orange, would also be part of the Fruit class but has different attributes of taste, colour and size from an apple.

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