CSC 480Software Engineering

OOAD Process

Topics

Overview: OOAD Process The object model Identifying classes Responsibilities and collaborations Hierarchy: inheritance and aggregation

Macro Development Process

The process can be roughly divided into three major phases

Analysis: focusing on what are required Design: answering the questions of how to fulfill

the requirements Resulting in blueprints that map functional needs to

program units (interrelated classes) Implementation: realizing the design with a

working system

Down to the Ground-LevelIdeas

Needs statement

Functional spec(D-req’ts)

Design docs

System in production System under dev.

Prototypes

High-up in the air

Solidground

Analysis

Design

Implementation

Conceptualization

C-req’ts

Analysis Phase

Specify system needs in a conceptual model High-level, with details omitted Document: system requirement specification (SRS)

Completeness a contract between client and developers

Consistency: without contradiction Readability: customer & developer (C-&D-) req’ts Addressing all shareholders interests Testability: can be tested against reality

Requirements Engineering

There is no clear-cut boundary between phases In OOA process, use cases are a powerful

means to present and organize requirements RUP claims to be use-case-driven Good for revealing both external and internal needs

(user and system requirements) Can be used for design, implementation, testing, and

user training purposes

The Design Phase

The goal is to find and present a solution The key is decomposition

Interrelated classes: class responsibilities collaborations Focusing on architecture (key classes + interfaces), omitting

implementation details

The outcome is system design document (SDD) Class diagrams Sequence diagrams State diagrams

Design Phase

Also known as high-level design Classes at various levels of abstraction Relationships among classes

Dependency Inheritance aggregation

Product design or UI design may be needed Story-boarding Screen navigation charts

Implementation Phase

Better known as the construction phase Detail design: sub-class level

Data structures, algorithms

Coding Unit testing Gradual integration and repeated “system” testing Deployment

Object and Class

An object is characterized by its State: Behavior: Identity

A class specifies objects with the same behavior An instance of a class is an object that belongs

to the given class

Micro Development Process

Largely driven by the stream of scenarios and architectural products Identifying classes and objects Identifying semantics of classes and objects Identifying the relationships among classes and

objects Implementing classes and objects

Identifying Classes

A rule of thumb is to look for nouns in SRS Class candidates usually fall in following categories

Tangible things Agents Events and transactions Users and roles Systems System interfaces and devices Foundational classes

Identifying Responsibilities

Responsibilities can be mapped to a functional requirement

Responsibilities include Things an object need to know: state Operations an object can perform: behavior

Assign a responsibility to exactly one class Assign responsibilities as evenly among classes

as possible

Identifying Relationships

Relationship types Hierarchical

Inheritance Aggregation

Association Dependency: aka collaborations

Object Collaborations

An object tends to fulfill its responsibilities by collaborating with other objects

Client-server contract Client: the object receiving a service Server: the object providing the service Contract: the interface definition through which a

service may be requested The client and server roles may change in different

collaborations