ObjectOriented OO Analysis and Design

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Object-Oriented (OO)Analysis and Design

• Keng Siau
• University of Nebraska-Lincoln
• College of Business Administration

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Introduction to OO Analysis and Design

• OO concepts arise from developments in OO
  programming
• Combine aspects of both ERDs and DFDs
• Claimed to be better than structured approaches
  to systems analysis and design
• maintenance
• adaptation
• redesign
• reuse

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Object Oriented Concepts

• 6 basic ideas in OO programming
• objects
• classes
• messages
• encapsulation
• inheritance
• polymorphism

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Objects

• A computer representation of some real-world
  thing or event (e.g., Keng Siau)
• Objects can have both attributes (e.g., SSN, age)
  and behaviors (e.g., teaching style, quiz style)
• Other example
• Object -- Rolls Royce
• Attributes -- Registration number, number of
  cylinders
• Behaviors -- lights go on, lights go off

5
Classes

• A category of similar objects
• Objects are grouped into classes
• Examples
• MIS Professors
• Management Professors
• Automobile

6
Messages

• Objects communicate through messages
• Example
• the class Operator is sending a message to an
  object (Jeep) of the class Automobile
• the message is Start Engine
• the classes Operator and Automobile have been
  carefully programmed to send and receive a Start
  Engine message

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Encapsulation

• Information about an object is encapsulated by
  its behavior
• An object maintains data about the real-world
  things it represents in a true sense
• Encapsulated data can be protected in such a way
  that only the object itself can make changes
  through its own behavior
• objects are reliable and consistent

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Inheritance

• One class can be created out of another class
• Parent class is known as a base class or
  superclass
• Child class is known as a derived class or
  subclass
• The derived class inherits all of the attributes
  and behaviors of the base class

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Polymorphism

• A message may have different effects depending on
  exactly what class of object receives the message
• Polymorphism refers to alternative behaviors
  among related derived classes
• An object can send a message to another object
  without necessarily knowing (or caring) the
  precise class to which the object belongs

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Polymorphism

• Example
• the message move is sent to an animal object,
  without knowing whether that object is a fish, a
  bird, a snake, or a mammal
• each of these animals knows how to interpret and
  carry out the move message -- e.g., swimming,
  flying, wiggling, or walking

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Object Oriented Analysis

• OO analysis by Coad and Yourdon is based on a
  five-layer model
• class/object layer
• structure layer
• service layer
• attribute layer
• subject layer

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Five-Layer OO Analysis

• Class/Object Layer
• denotes the classes and objects
• Structure Layer
• captures various structures of classes and
  objects (e.g., one-to-many relationships and
  inheritance)
• Service Layer
• denotes messages and objects behaviors

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Five-Layer OO Analysis

• Attribute Layer
• details the attribute of classes
• Subject Layer
• divides the design into implementation units or
  team assignments