object-oriented systems development:development

Object-Oriented Systems Development Bahrami ? Irwin/ McGraw-Hill

Chapter 4:Object-Oriented Methodologies

Object-Oriented SystemsObject-Oriented SystemsDevelopmentDevelopment:Using the Unified ModelingUsing the Unified ModelingLanguageLanguage

•Object-Oriented Methodologies–The Rumbaugh et al. OMT–The Booch methodology– Jacobson's methodologies

Goals (Con’t)

•Patterns•Frameworks•Unified Approach (UA)• layered Architecture

Basic Definitions•A methodology is explained as the

science of methods.•A method is a set of procedures in

which a specific goal isapproached step by step.

Too Many Methodologies•1986: Booch came up with the

object-oriented design concept,the Booch method.•1987: Sally Shlaer and Steve

Mellor came up withthe concept of therecursive design approach.

Too Many Methodologies (Con’t)•1989: Beck and Cunningham came up

with class-responsibility-collaboration (CRC) cards.

•1990: Wirfs-Brock, Wilkerson, andWiener came up with responsibility-driven design.

•1991: Peter Coad and Ed Yourdondeveloped the Coad lightweight andprototype-oriented approach.

Too Many Methodologies (Con’t)•1991: Jim Rumbaugh led a team at

the research labs of General Electricto develop the object modelingtechnique (OMT).•1994: Ivar Jacobson introduced the

concept of the use case.

Survey of Some of the Object-Oriented Methodologies

•Many methodologies are available tochoose from for system development.• Here, we look at the methodologies

developed by Rumbaugh et al.,Booch, and Jacobson which are theorigins of the Unified ModelingLanguage (UML) and the bases of theUA.

Rumbaugh et. al.’s ObjectModeling Technique (OMT)

• OMT describes a method for theanalysis, design, and implementationof a system using an object-orientedtechnique.

OMT (Con’t)•OMT consists of four phases,

which can be performediteratively:–1. Analysis. The results are

objects and dynamic andfunctional models.–2. System design. The result is a

structure of the basicarchitecture of the system.

OMT (Con’t)

–3. Object design. This phaseproduces a design document,consisting of detailed objectsand dynamic and functionalmodels.–4. Implementation. This activity

produces reusable, extendible,and robust code.

OMT Modeling•OMT separates modeling into

three different parts:– 1. An object model, presented by the

object model and the datadictionary.– 2. A dynamic model, presented by

the state diagrams and event flowdiagrams.– 3. A functional model, presented by

data flow and constraints.

OMT Object Model

numberbalancedepositwithdrawcreateTransaction

Account

Withdraw

CheckingAccount

transDatetransTimetransTypeamountpostBalance

Transaction

AccountTransaction

firstNamelastNamepinCode

Client

ClientAccount

CheckingSavingAccountSavingsAccount

OMT Dynamic Model

Nothing is selected

No account has been selected

Account has beenselected

Select Checkingaccount

Select Checking orsaving account

Select transactiontype (withdraw,

deposit, transfer)Enter the amount

Confirmation

OMT Functional Model

Client Account

CardReader PIN Code Process PIN Code

Process

DataStore

DataFlow

ExternalEntity

The Booch Methodology•The Booch methodology covers

the analysis and design phases ofsystems development.•Booch sometimes is criticized for

his large set of symbols.

The Booch Methodology (Con’t)•The Booch method consists of the

following diagrams:–Class diagrams–Object diagrams– State transition diagrams–Module diagrams– Process diagrams– Interaction diagrams

The Booch Methodology (Con’t)

colormanufacturercost

Escort

Mustang Taurus

inherits

superclass

Silenced Sounding

Disabled

Enabled

SoundAlarm

SilenceAlarm

Enable Disable

Operator::TurnOffAlarm

AlarmFixed

•The Booch methodologyprescribes–A macro development process

–A micro development process.

The Macro Development Process•The macro development process

consists of the following steps:– 1. Conceptualization– 2. Analysis and development of the

model.– 3. Design or create the system

architecture.– 4. Evolution or implementation.– 5. Maintenance.

The Micro Development Process•The micro development process

consists of the following steps:– 1. Identify classes and objects.– 2. Identify class and object semantics.– 3. Identify class and object

relationships.– 4. Identify class and object interfaces

and implementation.

The Jacobson et al. Methodologies•The Jacobson et al. methodologies

(e.g., OOBE, OOSE, andObjectory) cover the entire lifecycle and stress traceabilitybetween the different phases.

Use Cases•Use cases are scenarios for

understanding system requirements.•A use case is an interaction between

users and a system.•The use-case model captures the

goal of the user and theresponsibility of thesystem to its users.

•The use case description mustcontain:–How and when the use case begins

and ends.– The interaction between the use case

and its actors, including when theinteraction occurs and what isexchanged.

Use Cases (Con’t)

–How and when the use case willstore data in the system.– Exceptions to the flow of events.

Library

Checking out books

Doing research

Reading books,NewspapersMember

SupplierPurchasing Supplies

Getting anInterlibrary loan

Object-Oriented SoftwareEngineering: Objectory

•Object-oriented softwareengineering (OOSE), also calledObjectory, is a method of object-oriented development with thespecific aim to fit thedevelopment of large, real-timesystems.

Objectory (Con’t)•Objectory is built around several

different models:–Use case model.–Domain object model.–Analysis object model.

Implementation model.– Test model.

Object-Oriented BusinessEngineering (OOBE)

•Object-oriented businessengineering (OOBE) is objectmodeling at the enterprise level.• Use cases again are the central

vehicle for modeling, providingtraceability throughout thesoftware engineering processes.

Structured byRealized by

Implemented by

Tested inExpress in

Use-case model

Domain Objectmodel

Analysismodel

Design model Implementationmodel

Testing model

OKNOT OK

OOBE (Con’t)

•OOBE consists of :–Analysis phase–Design– Implementation phases and– Testing phase.

Patterns•A pattern is an instructive

information that captures theessential structure and insight of asuccessful family of provensolutions to a recurring problemthat arises within a certain contextand system of forces.

•The main idea behind usingpatterns is to providedocumentation to help categorizeand communicate about solutionsto recurring problems.• The pattern has a name to

facilitate discussion and theinformation it represents.

Patterns (Con’t)

•A good pattern will do thefollowing:• It solves a problem. Patterns

capture solutions, not just abstractprinciples or strategies.• It is a proven concept. Patterns

capture solutions with a trackrecord, not theories or speculation.

Patterns (Con’t)

•The solution is not obvious. Thebest patterns generate a solutionto a problem indirectly—anecessary approach for the mostdifficult problems of design.• It describes a relationship. Patterns

do not just describe modules, butdescribe deeper system structuresand mechanisms.

Patterns (Con’t)

•The pattern has a significanthuman component.

•All software serves humancomfort or quality of life; the bestpatterns explicitly appeal toaesthetics and utility.

Patterns (Con’t)

Capturing Patterns•Guidelines for capturing patterns:– Focus on practicability.–Aggressive disregard of originality.–Nonanonymous review.–Writers' workshops instead of

presentations.–Careful editing.

Frameworks•A framework is a way of

presenting a generic solution to aproblem that can be applied to alllevels in a development.•A single framework typically

encompasses several designpatterns and can be viewed as theimplementation of a system ofdesign patterns.

•Design patterns are more abstractthan frameworks.•Design patterns are smaller

architectural elements thanframeworks.•Design patterns are less specialized

than frameworks.

Differences Between DesignPatterns and Frameworks

The Unified Approach•The idea behind the UA is not to

introduce yet anothermethodology.•The main motivation here is to

combine the best practices,processes, methodologies, andguidelines along with UMLnotations and diagrams.

Documentation & Traceability

of use-cases,analysis,

design, UI,and past

ExperiencesPatterns

Repository

UML BasedModeling

ConstructionComponentBasedDevelopment

User satisfactionusability tests,quality assurancetest

Continuous Testing

RefineanditerateIdentify Actors

Develop Use-Cases, activitydiagrams

Developinteractiondiagrams

Identify classes,relationships,attributes &methods

Continuous Testing

Designv viewand accessLayers andprototypes

Apply DesignAxioms

Design classes,their attributes,methods,association,structure ...

User satisfaction &Usability tests based on use casesBuild UML class

diagram

O-O Analysis

O-O Design

LayeredApproach

prototyping

The Unified Approach (UA)•The unified approach to software

development revolves around (butis not limited to) the followingprocesses and components.

UA Processes (Con’t)

•The processes are:–Use-case driven development.–Object-oriented analysis.–Object-oriented design.– Incremental development and

prototyping.–Continuous testing.

UA Methods and Technology•The methods and technology

employed includes:–Unified modeling language (UML)

used for modeling.– Layered approach.–Repository for object-oriented

system development patterns andframeworks.– Promoting Component-based

development.

UA Object-Oriented Analysis:Use-Case Driven

•The use-case model captures theuser requirements.•The objects found during analysis

lead us to model the classes.•The interaction between objects

provide a map for the designphase to model the relationshipsand designing classes.

UA Object-Oriented Design• Booch provides the most comprehensive

object-oriented design method.•However, Booch methods can be

somewhat imposing to learn andespecially tricky to figure out where tostart.

• UA realizes this by combining Jacobsonet al.'s analysis with Booch's designconcept to create a comprehensive designprocess.

Iterative Development andContinuous Testing

•The UA encourages theintegration of testing plans fromday 1 of the project.•Usage scenarios or Use Cases can

become test scenarios; therefore,use cases will drive the usabilitytesting.

Modeling Based on the UnifiedModeling Language

•The UA uses the unified modelinglanguage (UML) to describe andmodel the analysis and designphases of system development.

The UA Proposed Repository•The requirement, analysis, design, and

implementation documents should bestored in the repository, so reports canbe run on them for traceability.•This allows us to produce designs that

are traceable across requirements,analysis, design, implementation, andtesting.

The Layered Approach toSoftware Development

•Most systems developed withtoday's CASE tools or client-serverapplication developmentenvironments tend to lean towardwhat is known as two-layeredarchitecture: interface and data.

Two-Layer Architecture• In a two-layer system, user

interface screens are tied directlyto the data through routines thatsit directly behind the screens.

Workstation

TitleAddress

Problem With the Two-LayerArchitecture

•This approach results in objectsthat are very specialized andcannot be reused easily in otherprojects.

Three-Layer Architecture•Your objects are completely

independent of how:– they are represented to the user

(through an interface) or– how they are physically stored.

Workstation

TitleAddress

User Interface layerThis layer is typically responsible

for two major aspects of theapplications:•Responding to user interaction•Displaying business objects.

Business Layer•The responsibilities of the

business layer are very straight-forward:•model the objects of the business

and how they interact toaccomplish the businessprocesses.

Business Layer: Real Objects(Con’t)

These objects should not beresponsible for:• Displaying details• Data access details

Access Layer•The access layer contains objects

that know how to communicatewith the place where the dataactually resides,•Whether it be a relational

database, mainframe,Internet, or file.

Access Layer•The access layer has two major

responsibilities:• Translate request• Translate result

Three-Layered Architecture

BusinessLayer

ViewLayer

Access Layer

Summary•we looked at current trends in

object-oriented methodologies,which have been towardcombining the best aspects oftoday's most popular methods.

Summary (Con’t)•Each method has its strengths.

Rumbaugh et al. have a strong methodfor producing object models.• Jacobson et al. have a strong method

for producing user-driven requirementand object-oriented analysis models.•Booch has a strong method for

producing detailed object-orienteddesign models.

•Each method has weakness, too. WhileOMT has strong methods for modelingthe problem domain, OMT modelscannot fully express the requirements.• Jacobson, although covering a fairly

wide range of the life cycle, does nottreat object-oriented design to the samelevel as Booch, who focuses almostentirely on design, not analysis.

Summary (Con’t)

Summary (Con’t)•The UA is an attempt to combine

the best practices, processes, andguidelines along with UMLnotations and diagrams for betterunderstanding of object-orientedconcepts and object-orientedsystem development.

object-oriented systems development:development

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