Lecture 3.1 Introduction to OOAD

8/4/2019 Lecture 3.1 Introduction to OOAD

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Object-orienAnalysis and Des

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OO Analysis and Design - 2

References

Object-Oriented Analysis and Design withApplications (2nd Edition)

Grady Booch

Addison-Wesley Professional

Thinking in Java

Bruce Eckel

Freely downloadable athttp://www.mindview.net/Books/TIJ/


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Object-oriented Analysis

Object-oriented Analysis is concerned withdeveloping software requirements andspecifications that are expressed

in terms of objects

instead of to the traditional data or functionalviews of systems


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Complexity

Is an essential property of any computer-based system

Why?

Problem to be solved might be very complex

Issues in project management

Software is perceived as being very malleableetc.


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Managing complexity

Is difficult

Our brain can only focus on 72 things at a time

The solution is to

Decompose the problem into abstractions

And hierarchise those abstractions


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Obect-Oriented Design

Object-oriented design is concerned withdeveloping an Object-Oriented model of asoftware system to implement the identified

requirements and specificationsidentified during Object-Oriented Analysis


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Object-Oriented Design

Is both artistic and scientific

The final objective is to produce a model

RequiresA notationUML = Unified Modeling Language

A methodology

UP = Unified Process (or, rather, Simplified UP)

Tools


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The object

Has

An identity

A parallel can be made with the primary key concept

A stateSet of all the private attributes of the object

A behaviour

How does the object react when receiving a message?


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An Object-Oriented model

Has the following essential caracteristics

Abstraction = class

Encapsulation

Two types of hierarchies

has-a = association

is-a = inheritance


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Abstraction = class

Template from which objects are created(instanciation)

Only relevant details are taken into account

Hence abstraction

We focus only on the behaviour

we do not care about the state (private attributes)

we care about the interface (public methods)


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Encapsulation

Implementation is hidden

Attributes are not visible from the outside

Decoupling the interface from the implementation


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Has-a hierarchy : association

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Importance of association

Main caracteristics

Shows that an object from one class possesses oruses object(s) from another class

The lifetime of participating objects are notnecessarily linked

Somewhat similar in relationships in the ER model

One important difference is that the relationship can beunidirectional when doing OO modeling


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Has-a hierarchy : aggregation

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Importance of aggregation

Main features

Shows that some object can contain other objects

The lifetime of the participating objects are linked

In fact, they are the same

That is, when the controlling object is destroyed, anyenclosed object is also destroyed


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Is-a hierarchy : inheritance


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Importance of inheritance

Factoring behaviour

Creates an easily extensible model

Redefinitions are possibleOverloading is possible

POLYMORPHISM becomes possible

This is the most imporant aspect of OO

All OO models must exhibit inheritance


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Polymorphism


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Importance of polymorphism

Make the software

Simpler to write

Simpler to maintain and evolve

80% of existing programmers only do maintenance

Better performance because of compactness ofcode

Complete example of an OO modelClasses (and associated methods and attributes)used in a simulation of a solar system

Lecture 3.1 Introduction to OOAD

Documents

Transcript of Lecture 3.1 Introduction to OOAD