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Chapter 2: Introduction to Object-Oriented Systems Analysis and Design

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Objectives

Understand the basic characteristics of object-oriented systems.Be familiar with the Unified Modeling Language (UML), Version 2.0.Be familiar with the Unified Process.Understand a minimalist approach to object-oriented systems analysis and design.

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Basic Characteristics of Object Oriented Systems

Classes and ObjectsMethods and MessagesEncapsulation and Information HidingInheritancePolymorphism and Dynamic Binding

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Classes and Objects

Object-oriented approach uses self-contained modules called objects (containing both data and processes) as the building blocks for developing a system.An object is a thing, both tangible and intangible. Account, Vehicle, Employee, etc.

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Classes and Objects (Cont.)

To create an object inside the computer program, we must provide a definition for objects—how they behave and what kinds of information they maintain —called a class.

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Classes and Objects

Class – Template to define specific instances or objectsObject – Instantiation of a class (i.e. an instance of a class)Attributes – Describes the objectBehaviors – specify what object can do

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Classes and Objects

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Methods and Messages

Methods implement an object’s behaviorAnalogous to a function or procedure

Messages are sent to trigger methodsProcedure call from one object to the next

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Messages and Methods

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Sending a Message

deposit 250.00

Message deposit with the argument 250.00 is sent to a BankAccountobject SV198.

Message deposit with the argument 250.00 is sent to a BankAccountobject SV198.

SV198 : BankAccount

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Sending a Message and Getting an Answer

current balance

getCurrentBalance()

Ask for the current balance of this particular account.

Ask for the current balance of this particular account.

SV198 : BankAccount

The current balance of SV198 is returned.

The current balance of SV198 is returned.

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Calling a Class Method

maximum speed

MobileRobot

getMaximumSpeed()

Ask for the maximum possible speed for all MobileRobot objects is returned.

Ask for the maximum possible speed for all MobileRobot objects is returned.

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Encapsulation and Information Hiding

Encapsulation combination of data and process into an entity

Information HidingOnly the information required to use a software module is published to the user

Reusability KeyUse an object by calling methods

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Inheritance

Superclasses or general classes are at the top of a hierarchy of classesSubclasses or specific classes are at the bottomSubclasses inherit attributes and methods from classes higher in the hierarchy

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Inheritance

Inheritance is a mechanism in OOP to design two or more entities that are different but share many common features.

Features common to all classes are defined in the superclass.The classes that inherit common features from the superclass are called subclasses.

We also call the superclass an ancestor and the subclass a descendant.

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Class Hierarchy

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Inheritance

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Polymorphism and Dynamic Binding

PolymorphismA message can be interpreted differently by different classes of objects

Dynamic BindingSometimes called late bindingDelays typing or choosing a method for an object until run-time

Static BindingType of object determined at compile time

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Polymorphish & Encapsulation

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The Unified Modeling Language, Version 2.0

Structure DiagramsBehavior DiagramsExtension MechanismsDevelopers

Grady BoochIvar JacobsonJames Rumbaugh

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Structure Diagram

Structure Diagrams includeClassObjectpackageDeploymentComponentComposite structure diagrams

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Structure Diagrams

Classrelationship between classes

ObjectRelationships between objects

PackageGroup UML elements together to form higher level constructs

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Structure Diagrams Cont.

DeploymentShows the physical architecture and software components of system

ComponentPhysical relationships among software components

Composite StructureIllustrates internal structure of a class

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Behavior Diagrams

ActivityIllustrates business workflows

SequenceTime-based ordering Behavior of objects activities in a use case

CommunicationCommunication among a set of collaborating objects of an activity

Interaction Overview TimingOverview of flow of control of a process

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State Machines

Behavioral State MachineExamines behavior of one class

Protocol State MachineShows dependencies of different interfaces of a class

Use-CaseCaptures business requirementsIllustrates interaction between system and environment

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Use Case Diagrams

Captures Business requirementsIllustrates interaction between a system and its environment

Includes end userAny external system that interacts with its information system

Documents and clarifies requirements of system being modeled

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Extension Mechanisms

StereotypesGives ability to incrementally extend UML

Tagged ValuesAdd new properties to base elements

ConstraintsPlace restrictions on use of model elements

ProfilesGroup model elements into a package

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Object-Oriented Development Approaches

• Use-case driven• Architecture Centric

• Functional view, static view, and dynamic view.

• Iterative and Incremental

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Benefits of the Object Approach

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The Unified Process

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Supporting Workflows

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A Minimalist Approach

Benefits of Object-Oriented Systems Analysis and DesignExtensions of the Unified ProcessThe Minimalist Object-Oriented Systems Analysis and Design Approach

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MOOSAD Approach

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Summary

Basic characteristics of an object oriented systemUnified modeling LanguageUnified modeling systemObject oriented Systems Analysis and DesignMinimalist approach to Object oriented systems analysis and design with UML