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Chapter 0 : Introduction to Object Oriented Design.

Chapter 0 : Introduction to Object Oriented Design. The science of computing. computer science is a science of abstraction – creating the right model for a problem and devising the appropriate mechanizable techniques to solve it. — A. Aho and J. Ullman. Objectives.

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Chapter 0 : Introduction to Object Oriented Design.

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  1. Chapter 0 : Introduction to Object Oriented Design.

  2. The science of computing • computer science is a science of abstraction – creating the right model for a problem and devising the appropriate mechanizable techniques to solve it. — A. Aho and J. Ullman NH-Chapter 0

  3. Objectives • After studying this chapter you should understand the following: • the nature of software systems; • how abstraction and decomposition are used to deal with complexity in problems; • the fundamental components of a program, data and functionality; • objects, and object-oriented systems and their relationship to software systems in general. NH-Chapter 0

  4. Objectives • Also, you should be able to: • identify basic components in complex structures; • provide examples of abstraction levels from least abstract to more abstract; • explain how composition and abstraction simplify the organization of a system; • provide informal algorithms for common activities. NH-Chapter 0

  5. Nature of a software system • A software system is a temporary solution to a changing problem. • With two fundamental characteristics: • they are dynamic • they are complex. NH-Chapter 0

  6. Dealing with complexity: composition and abstraction • Size of software system • must be broken down into manageable pieces • Must be dealt with as a compositestructure. • Parts must interact together. • The more parts the more interaction. • System complexity is proportional to the number of parts. NH-Chapter 0

  7. Dealing with complexity: composition and abstraction • composition: process of building a system using simpler parts or components NH-Chapter 0

  8. Dealing with complexity: composition and abstraction • Abstraction: can deal with system components with no worry about details of how components are constructed. • abstraction: • process of ignoring details irrelevant to problem at hand • Emphasizes essential ones. • To abstract is to disregard certain differentiating details. NH-Chapter 0

  9. Two aspects of a system: data and functionality • data –information program deals with • data descriptions are fixed, • individual data values change each time program runs NH-Chapter 0

  10. Two aspects of a system: data and functionality • functionality – what the program does with data. • computation: a goal-directed sequence of actions performed by a processor. • algorithm: set of instructions describing pattern of behavior guaranteed to achieve a goal. NH-Chapter 0

  11. Object-oriented systems • Use the Object Oriented approach for structuring systems. • Intended to produce systems that are: • composite, • modular • built using abstraction, • organized around data. NH-Chapter 0

  12. Object-oriented systems • Objects: abstractions used to describe the problem. • Functionality of system is distributed to the objects. • Each object has algorithms to accomplish specific tasks. NH-Chapter 0

  13. Summary • Software systems are complex; and • Systems change over time. • To address these difficulties, • make extensive use of abstraction; • build systems that are modular, and composite. NH-Chapter 0

  14. Summary • To define a software system, include • a description of the data items to be manipulated by the system, and • a collection of algorithms that provide the system’s functionality. • The object-based methodology we adopt structures the system around the data. NH-Chapter 0

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