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ood - LESSON 7 Object Oriented Software Design Contents...

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LESSON 7 Object Oriented Software Design Contents Objective 1. To understand the concept of Object Oriented Design 2. To apply Object Oriented Principles to design software systems. 3. To understand what the Unified Modeling Language (UML) is. 4. Be able to identify the components of Unified Modeling Language (UML) diagram. 5. Be able to identify the Unified Modeling Language (UML) notations for a class. 6. Be able to define a class diagram using UML. 7. Be able to develop and code a UML class diagram into a complete program. Introduction Object-oriented design (OOD) is the philosophy of developing an object-oriented model of a software system, by defining the classes and their interactions with one another. The major benefits of OOD are easy maintainability systems, easy understandable systems, easy expandable systems, and reusable components of the systems,. In this lesson you will learn about the principles of OOD through the design principle called Unified Modeling Language (UML). First we will learn what UML is, and how it relates to classes. Secondly, we will learn how it is used to model the solution to an entire system by using class diagrams. When you are designing classes, you should pay attention to those units that are highly related to each entity. One way to achieve this is by applying the concept of cohesion. The third concept that will be covered is the principle of cohesion. This will be followed by the concept of coupling – the relationship among objects. The lesson closes with a survey of misinterpretations and pitfalls that could occur during the design and implementation phases. Before studying the pitfalls, however, we will develop an entire system using the concept of Object Oriented Design along with the Uniform Modeling Language. Uniform Modeling Language (UML) The Unified Modeling Language ( UML ) is a standardized specification language that uses a set of diagrams for modeling objects, with the ultimate aim of solving problems. UML feature several types of diagrams for different purposes, six of which are component diagrams, composite structure diagram , d eployment diagram , object diagram , package diagram , and class diagram . Of these diagrams, class diagram is the one of importance to this lesson. Class Notation
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Central to the UML notation is the concept of a class. Class as we know it is a blue print that models an entity. It has name, attributes and operations. In UML notation, a class is represented by a rectangle that is divided into three regions. The first region specifies the name of the class, the second region specifies the fields – instance variables, class variables, and constants – and the third region specifies the methods. Figure 6.1 shows a schematic view of class notation using UML .
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