OOSE3 OOSE in Real World and Industry

8/8/2019 OOSE3 OOSE in Real World and Industry

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Object OrientedObject Oriented

Software EngineeringSoftware Engineering# 4

Prof. Dr.Prof. Dr. O.P.VyasO.P.VyasM.TechM.Tech. ( Computer Sc. ) IIT. ( Computer Sc. ) IIT KharagpurKharagpur

Ph.D. (Computer Sc) IITPh.D. (Computer Sc) IIT KharagpurKharagpur

DAAD Fellow (Germany), AOTS Fellow(Japan)DAAD Fellow (Germany), AOTS Fellow(Japan)

Professor & Program Coordinator(SE)Professor & Program Coordinator(SE)Indian Institute of Information Technology, AllahabadIndian Institute of Information Technology, Allahabad


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Prof.Dr. O.P.Vyas3.2Data Mining

Significant S/W projects & OSE approachSignificant S/W projects & OSE approach

Data & Knowledge Engineering

Data Base Connectivity approaches

Data Mining & Business Intelligence Projects?

Software Project for Mobile devices

Functional & Non-functional requirements

Feature Phone Vs Smartphone S/W:OSE approach

Service Oriented Architectures

SOA & Cloud computing solutions

Framework Requirements

OOSE Implementations: Which concepts to use?OOSE Implementations: Which concepts to use?

When & How: Inheritance,Polymorphism2


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Market Market requiresrequires InnovationInnovation

InnovationInnovation requiresrequires ResearchResearch

&&

Research requiresResearch requires concerted effort concerted effort


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Data & Knowledge Engineering: OSE approachData & Knowledge Engineering: OSE approach

DBMS applications: Two Tier or Three tier approachDBMS applications: Two Tier or Three tier approach

Front-End Vs Back End

Data Base Connectivity

Data & Knowledge Engineering: Data Mining ?Data & Knowledge Engineering: Data Mining ?

Data Mining: Characteristics

DM applications: Functionalities.

Developing Business Intelligence Projects

OOSE Implementations: Which concepts to use?OOSE Implementations: Which concepts to use?

When & How: Inheritance,Polymorphism

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Data & Knowledge EngineeringData & Knowledge Engineering--Chronological Dev.Chronological Dev.

Evolutionary steps Business queryBusiness query Enabling technologiesEnabling technologies Product vendorsProduct vendors Characteristics

Data Collection(1960s)

What was my totalrevenue in the last

five years

Computers, tapes,disks IBM Retrospective,Retrospective, staticdata delivery

Data Base

(1980s)

What were A.C unit

sales in New England

last March?

Relational

Databases, SQL,

ODBC

Oracle, Sybase, Informix,

IBM,MicrosoftRetrospectiveRetrospective

dynamic data delivery

at record level.

Data Warehousing

& Decision support

systems1990s)

What were A.C.unit

sales in New England

last March?Drill down

to Boston.

OLAP, Multi -

dimensional

databases, DW

Pilot, Comshare,Arbor,Cognos,Microstrategy.

Retrospective,Retrospective,

dynamic data delivery

at multiple levels.

Data Mining

(Emerging )

Whats likely to

happen to Bostons

A.C.unit sales next

month? Why ?

Advanced algorithms,

Machine Learning

approaches, massive

databases.

Pilot, Lockheed, IBM,SGI, Mineset etc.

Prospective,Prospective,

proactiveproactive information

delivery.


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Database ArchitectureDatabase Architecture

The architecture of a database systems is greatly influenced bythe underlying computer system on which the database is

running:

Centralized

Client-server

Parallel (multiple processors and disks)

Distributed

Data Base Application Architecture can be categorized asData Base Application Architecture can be categorized as

TwoTwo--TierTierand Three Tier ArchitectureThree Tier Architecture


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Database Application ArchitecturesDatabase Application Architectures

(web browser)(web browser)

OldOld ModernModern


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DBMS Project TeamDBMS Project Team

Data Specialists--> Modeler

--> Architect

Developers

FRONT END(VB, VC++, JAVA)

DBAs

BACK END( Oracle,

SQL-Server, DB-2)

Project Leader


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Data Mining & Knowledge DiscoveryData Mining & Knowledge Discovery


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Knowledge Discovery in Databases (KDD)Knowledge Discovery in Databases (KDD)

Technology: ProcessTechnology: Process

Adapted from[Fayyad, Piatetsky-Shapiro, and Smyth, 1996]

Data MiningData Mining

KnowledgeKnowledge

DiscoveryDiscovery


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Knowledge Discovery & BI implementationsKnowledge Discovery & BI implementations


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Data MiningAlgorithm

Score model

model

Results Pattern

Data Mining Systemtraining

evaluation

prediction

Historical Training data

New data

Data set

Data Mining Mechanism


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Machine Learning ApproachMachine Learning Approach

An unprecedented wealth of data is being generated

The demands and opportunities for interpreting these data are expanding more thanever.

Machine learning is one of the most popular approach to build Theory from the fielddata.

Machine learning approaches are ideally suited for areas in which there is a lot of data

but little theory.

On the theoretical side , a unifying framework for all machine learning methods hasemerged since late 1980s. This is the Bayesian probabilisticBayesian probabilistic framework for modelingand inference

The goal in machine learning is to extract useful information from a body of data bybuilding good probabilistic models and to automate the process as much as possible.

Will traditional OSE Approaches work fine with Machine Learning applications ?


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Data MiningData Mining

What kind of data

Biological Spatial Text Multimedia

RDBMS DataWarehouse Special WebData

OOD Time

Series

Legacy


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Data Mining

ClusteringClustering

AnalysisAnalysis

AssociationAssociation

MiningMining

A:R:M:Techniques

Applicationdomain

ClassificationClassification

ClassificationTechniques

Asso.Classifiers

Data Mining FunctionalitiesData Mining Functionalities


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Business Intelligence projects & OSEBusiness Intelligence projects & OSE

For Association Rule Mining: MBA

Algorithms for ARMAlgorithms for ARM

For Classification and Predictive Analytics

Learning & PredictingLearning & Predicting

For Clustering Analysis & Outlier Discovery

Descriptive approachDescriptive approach

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What is Market Basket Analysis?What is Market Basket Analysis?

Customer AnalysisCustomer Analysis

Market Basket Analysis uses the information about

what a customer purchases to give us insight into

who they are and why they make certain purchases. Product AnalysisProduct Analysis

Market basket Analysis gives us insight into the

merchandise by telling us which products tend to be

purchased together and which are most amenable topurchase.


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Market BasketMarket Basket Analysis S/W ProjectAnalysis S/W Project

Is soda typically purchased with bananas?Does the brand of soda make a difference?

Where should detergents be placed in theStore to maximize their sales?

Are window cleaning products purchasedwhen detergents and orange juice are

bought together?

How are the demographics of theneighborhood affecting what customers

are buying?

?

?

?

?


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Companies using Business IntelligenceCompanies using Business Intelligence

Burger KingBurger King that has restaurants in 11,435 locations in 58 countrieswith annual sales of $11.3 billion is using Business Objects

ofBusiness Intelligence to help them achieveoperational excellence throughout their organization, and maintain

their leadership in a competitive industry

Wal Mart

Wal-Mart is often described as a pioneering leader in data mining &data management S/W applications:

Wal-Mart captures point-of-sale transactions from over 2,900 stores in

six countries and continuously transmits this data to its massive7.5 terabyte data warehouse.Wal-Mart allows more than 3,500 suppliers to access data on their

products and perform data analyses. These suppliers use this data toidentify customer-buying patterns at the store display level.

They use this information to manage local store inventory andidentify new merchandising opportunities.


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DataData MiningMining B.I. ApplicationsB.I. Applications

Master Card

MasterCard International uses data mining to extract statistics about its millions of dailycardholder transactions; furthermore, MasterCard sell this data to its 20,000 business

partners banks and other companies, such as Shell Oil, that offer credit-card

services.

Internet Web Surf-Aid (Web Mining)

IBM Surf-Aid applies data mining algorithms to Web access logs for market-relatedpages to discovercustomer preference and behavior pages, analyzing effectiveness ofWeb marketing, improving Web site organization, etc.

Sports

IBM Advanced Scout analyzed game statistics (shots blocked, assists, and fouls) togain competitive advantage for their Team.their Team.


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Examples of Discovered PatternsExamples of Discovered Patterns

Association rules: find rules between different attributes

86% of Bread-Butter buyers are not Noodles customers but both are buyingTomato ketchup with 95% of customer base.

98% of AOL users also have E-trade accounts

Classification: Classify data based on the values in a classifying attribute

People with age less than 40 and salary > 40k trade on-line

Clustering: Group data to form new classes

Users A and B access similar URLs

Outlier Detection

Person A is showing sudden high increase in his Cholesterol !

User A spends more than twice the average amount of time surfing on theWeb


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Examples of Predictive Analytics ProjectsExamples of Predictive Analytics Projects

Classifying whether the new credit card applicantnew credit card applicant

will be ofHighHigh, MediumMedium orLowLow credit risk.

Will be a perspective buyer of a particular new launch?

For a targeted campaign . Classifying credit card / telephone card transactions

as legitimatelegitimate orfraudulent.fraudulent.

Categorizing news stories as finance,

weather, entertainment, sports, etc

Predicting tumor cells as benignbenign ormalignantmalignant

Classifying secondary structures of protein

as alpha-helix, beta-sheet, or random

coil


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Constructing Classifier for B.I.Constructing Classifier for B.I.

The leading Credit Card Company Visa InternationalVisa International and Computer CompanyAcerAcerInc.Inc. has agreed to market the newly launched Laptop Computer.

For targeted marketing campaign, both the companies would like to use the

existing database of Visa Credit card holders, to find out most likely buyersmost likely buyers of

their Computer.

For a given Database, your job will be to construct a Classifier.Classifier. This Classifier should take an input as the customer-details like

I. Age,

II. Income

III. Student or ProfessionalIV. Credit_Card Ratings

And based on above inputs, the ClassifierClassifierwould PredictPredict, whether the person is

likely buyer of the Laptop Computer or not.


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Significant S/W projects & OSE approachSignificant S/W projects & OSE approach

Data & Knowledge Engineering DBMS & beyond

Data Base Connectivity: existing approaches

Software Projects for Mobile devices Functional & Non-functional requirements

OSE approach !

Service Oriented Architecture Recent Trends in SOA & Cloud Computing

Framework Requirements

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S/W project for Mobile DevicesS/W project for Mobile Devices

Applications for Mobile devices J2ME features !

Developing Smartphone Applications

Platform for SmartphonePlatform for Smartphone

Emulators

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Motivation & ChallengesMotivation & Challenges MotivationMotivation ::

Interest of user is switching towards new gadgets eg. Cell phones etc..

Today's Web demand dynamic and customizable capability in products.

Available technology:Available technology:

Develop a smooth finished application with look and feel Ex. mashupsolution for Smartphone.

Mashup provides the customizable capabilities to the user.

Challenges:Challenges:

Limited Memory

Low processing speed

No standardization

Small display


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SmartphoneSmartphone Smartphone is a mobile phone that offers more

advanced computing ability and connectivity than a

contemporary basic 'feature phone'. Smartphones and feature phones may be thought

of as handheld computers integrated within a

mobile telephone, but while most feature phones

are able to run applications based on platformsbased on platforms

such assuch as Java MEJava ME orBREW,(Binary Runtime

environment for Wireless)

Java Platform, Micro Edition, or Java ME, is a Java

platform designed for mobile devices and

embedded systems.

From mobile phones (especially feature phones)and set-top boxes. Java ME was formerly known as

Java 2 Platform, Micro Edition (J2ME).

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SmartphoneSmartphone

A Smartphone is a mobile phone that offers more advancedcomputing ability and connectivity than a contemporary basic feature

phone.

A smartphone allows the user to install and run more advanced

applications based on a specific platform.

Smartphones run complete operating system software providing a

platform for application developers.

What are the new breed of application paradigm required?

MashupMashup on mobile is very useful for people who use smart phone to

have an edge over other and gain business advantages.


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SmartphoneSmartphone

Smart phones are the future of the wireless industry.

It is an easy device to be used and give all the benefits of a laptop.

All Smartphone hardware and software data (iPhone, Android, Blackberry, HP/Palm

)is compiled at The Smartphone Genome Project

Smartphone popularity has been increased these days because of its portability and

usage.

Its also attracting many developer to use its platform for running many web

application.

Share of 2010 Q1 smartphone sales to end users by O.S.

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WidgetsWidgets

In computer programming, a widget (or control) is an element of a graphicalgraphical

user interfaceuser interface (GUI) that displays an information arrangement changeable by

the user, such as a window or a text box.

Widget is short for window gadget.

The defining characteristic of a widget is to provide a single interaction point for

the direct manipulation of a given kind of data. In other words, widgets are basic visual building blocks which, combined in an

application, hold all the data processed by the application and the available

interactions on this data.

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WidgetsWidgets

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A widget is a small application or piece of dynamic content

that can be easily placed into a web page

Widgets are known as different names by different vendorsdifferent names by different vendors:

gadgets, blocks, flakes

Widgets can be written in any language or and can be simply

HTML .

iWidget is the IBM standardization for widgets.

Widget?


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Application WidgetsApplication Widgets In the context of an application, a widget may be enabled or disabled at a given

point in time.

An enabled widget has the capacity to respond to events, such as keystrokesor mouse actions. A widget that cannot respond to such events is considered

disabled.

The appearance of disabled widget is typically different from an enabled

widget; the disabled widget may be drawn in a lighter color, or may be visually

obscured in some way. See the image to the right for an example. Widgets are sometimes qualified as virtual to distinguish them from their

physical counterparts, e.g. virtual buttons that can be clicked with a mouse

cursor, vs. physical buttons that can be pressed with a finger.

A related (but different) concept is the desktop widget, a small specialized GUI

application that provides some visual information and/or easy access tofrequently used functions such as clocks, calendars, news aggregators,

calculators and desktop notes. These kinds of widgets are hosted by a widget

engine.

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Structure of a WidgetStructure of a Widget

Widgets have a name

the name should be unique amongst all widgets.

the name should describe the function of the widget

the name of the widget will not be exposed, unless the widget decides to

do so

Widgets live within their own folder within the same server as Sakai this enables a widget to perform AJAX operations back to the sakai

instance.

Within the widget folder there will be an html page that contains the widget

There will be a css folder, a js folder and optionally an images folder.

During development you will use local copies of javascript and css contained

within the widget development kit

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MashupMashup : New breed of Web Applications: New breed of Web Applications

Mash-ups are part of an ongoing shift towards more a more interactive and

participatory Web ( Web 2.0 ) with more user-defined content and services.

In web development, a mashup is a web page or application that uses or

combines data or functionality from two or many more external sources to

create a new service.

Mash-ups are often created by using a development approach calledAjax.Ajax.

Mashup center solution is already running well on desktop environment.

Desktop resource availability gives us freedom to run a heavy process likemashup on it quite easily.

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MashupMashup centercenter

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Create new applications by reusing existing data andservices

Develop widgets from enterprise systems

Discoverand share mashups, widgets, feeds, andservices

Transform information into new feeds


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IBM Mashup CenterIBM Mashup Center

IBM Mashup Center is an end to end mashupplatform

enabling the rapid creation, sharing, anddiscovery of

reusable application building blocks(widgets, feeds, mashups) that can be easilyassembled into new applicationsOr leveraged within existing applications

delivering lower development costs, rapidROI, quick delivery ofdynamic applications,and greater productivity.


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Quickly Create and Share New Mashups

The mashup builder supports rapid assembly and sharing of mashup pages and spaces

without coding!

Rendering IBM-Mashup pages on mobile


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Developing projectsDeveloping projects

Business Intelligence solutions would require

Data Mining Algorithms

Pre-processed data for mining

OSE approach for

Project for Mobile devices

Emulators for the proposed work

Developing Widgets

Project on SOA

Using Framework for SOA

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Many ARM algorithmsMany ARM algorithms

There are a large number of them!! They use different strategies and data structures.

Their resulting sets of rules are all the same.

Given a transaction data set T, and a minimum support and a minimum confident, the

set of association rules existing in T is uniquely determined. Any algorithm should find the same set of rules although their computational

efficiencies and memory requirements may be different. We study only one: the

Apriori Algorithm


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Constructing Classifier for B.I.Constructing Classifier for B.I.

The leading Credit Card Company Visa InternationalVisa International and Computer CompanyAcerAcer

Inc.Inc. has agreed to market the newly launched Laptop Computer.

For targeted marketing campaign, both the companies would like to use the

existing database of Visa Credit card holders, to find out most likely buyersmost likely buyers of

their Computer.

For a given Database, your job will be to construct a Classifier.Classifier.

This Classifier should take an input as the customer-details like

I. Age,

II. Income

III. Student or Professional

IV. Credit_Card Ratings

And based on above inputs, the ClassifierClassifierwould PredictPredict, whether the person is

likely buyer of the Laptop Computer or not.


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UCI KDD ArchiveUCI KDD Archivehttp://kdd.ics.uci.eduhttp://kdd.ics.uci.edu

This is an online repository oflarge data sets which

encompasses a wide variety of datatypes, analysis tasks, and

application areas.

The prima

ry role ofthis reposi

tory is

to en

able rese

archers in

knowledge discovery and data mining to scale existing and

future dataanalysis algorithms to very large and complex data

sets.

. The archive is intended to serve as a permanent repository ofpublicly-accessible data sets for research in KDDand data

mining. It complements the original UCI Machine Learning

Archive , which typically focuses on smaller classification-

oriented data sets.


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SOA & F.I.SOA & F.I.

The Internet is a tremendous success story and with it the TCP/IPprotocols suite, which is the core technology of the Internet.

Using the Internet requires to use the TCP/IP protocols. Thus it is

hard to change or even modify these protocols.

Driven by the demands of ever emerging applications and thecapabilities of new communication networks, many workarounds

have been introduced, like sub-layer proliferation (e.g. MPLS at

layer 2.5, Ipsec at layer 3.5, and TLS at layer 4.5), and erosion of

the end-to-end model (middle-boxes, such as firewalls, NATs,

proxies, caches, etc.).

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SOASOA

A promising methodology is the service-oriented architecture(SOA) paradigm for organizing and utilizing distributed

capabilities that may be under the control of different ownership

domains .

In order to achieve loose coupling, protocols must not expose any

internal mechanisms.

This requires well defined interfaces, which reflect only the

service, i.e. the visible result, of a protocol.

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Layered ProtocolsLayered Protocols

No shared memory for data exchange

Use network to exchange messages

Problems:

What do the bits and bytes mean?

Where does a message start and end?

Has a message been lost?

Is the order of the messages received correct?

Solution: ISO OSI Reference Model

ISO = International Standards Organisation

OSI = Open Systems Interconnection

Models communication in open systems

Better understanding when problems arise

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SOASOA

Services are the central design elements of SOA.

The fundamental roles of a service-oriented architecture are the Service

Providers, the Service Consumers and the Service Brokers as shown in figure

1.

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SoASoA

Project develoment RequirementsSOA needs technical support

Technical University of Kaiserslautern (Germany)

Framework for the SOA

Network Functionality

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BB FrameworkBB Framework

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OOSE : Modeling & DesignOOSE : Modeling & Design

UML Diagrams provide the static and dynamic model of the system.

RoleRole andand LimitationsLimitations of UML !

A Class diagramClass diagram gives an overview of a system by showing its classes and the

relationships among them.

Class diagrams are staticstatic -- they display what interacts but notwhat interacts but not what happens

when they do interact.when they do interact. The classes represent entities with common features, i.e. attributes and

operations.

It is needful to decide

when to use Inheritance ,

When to use Association and

when the composition or Aggregation makes sense in

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UML with Rational RoseUML with Rational Rose

UML is a few different thingsfew different things toto different peopledifferent people. This comes bothfrom its own history and from the different views that people have

about what makes an effective software engineering process.software engineering process.

Rational Rose not only provides UML implementations but also

works as complete CASE tool. But still designing a good OOS project remains an issue involving

many parameters.

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UMLUML

A characterization ofthe three modes in which people use the UML:

1) sketch,

2) blueprint, and

3) programming language.

By far the most common of the three, is UML as sketch.

In this usage, developers use the UML to help communicate some aspects of

a system.

We can use sketches in a forward-engineering or reverse-engineering

direction. Forward engineering draws a UML diagram before you write code, while

reverse engineering builds a UML diagram from existing code in order to help

understand it.

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UML as BlueprintUML as Blueprint

In contrast, UML as blueprint is about completeness !

In forward engineering, the idea is that blueprints are developed by a designer

whose job is to build a detailed design for a programmer to code up.

That design should be sufficiently complete in that all design decisions are laid

out, and the programmer should be able to follow it as aprogrammer should be able to follow it as a pretty straightforwardpretty straightforwardactivity that requires little thought.

The designer may be the same person as the programmer, but usually the

designer is a more senior developerwho designs for a team of programmers.

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Software ArchitectureSoftware Architecture

SoftwareSoftware ArchitectureArchitecture defines the components of asystem, shows how they are packaged, and howhow

theythey interactinteract with one another.

The overall structure of the software and the ways in which thatThe overall structure of the software and the ways in which that

structure is,structure is, provides conceptual integrity for a systemprovides conceptual integrity for a system..

Shaw et al., Software Architecture

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Software Design TermsSoftware Design Terms

architecture the overall structure of the software

patterns conveys the essence of a proven design solution

abstraction data, procedure, control

refinement elaboration of detail for all abstractions

refactoring improve design without effecting behavior information hiding controlled interfaces

modularity compartmentalization of data and function

functional independence high cohesion and low coupling

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OOM design: User tipsOOM design: User tips

Hierarchy and factoring guidelines. A base class should not have too many

subclasses. If too many subclasses are derived from a single base class, thenit becomes difficult to understand the design. In fact, there should

approximately be no more than 7 2 classes derived from a base class at any

level.

Keeping message protocols simple. Complex message protocols are an

indication of excessive coupling among objects. If a message requires morethan 3 parameters, then it is an indication of bad design.

Number of Methods. Objects with a large number of methods are likely to be

more application-specific and also difficult to comprehend limiting the

possibility of their reuse. Therefore, objects should not have too many methods.

This is a measure of the complexity of a class. It is likely that the classeshaving more than about seven methods would have problems.

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OOSE design tipsOOSE design tips

Depth of the inheritance tree. The deeper a class is in the class inheritance

hierarchy, the greater is the number of methods it is likely to inherit, making itmore complex. Therefore, the height of the inheritance tree should not be very

large.

Response for a class. This is a measure of the maximum number of methods

that an instance of this class would call. If the same method is called more than

once, then it is counted only once. A class which calls more than about sevencalls more than about sevendifferent methodsdifferent methods is susceptible to errors.

Number of messages per use case. If methods of a large number of objects are

invoked in a chain action in response to a single message, testing and

debugging of the objects becomes complicated. Therefore, a single messagesingle message

should not result in excessive message generationshould not result in excessive message generation and transmission in asystem.

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Creating Quality Classes : Difficulties & RisksCreating Quality Classes : Difficulties & Risks

Modeling is particularly difficult skill Even excellent programmers have difficulty thinking at the

appropriate level of abstraction

Education traditionally focus more on programming than

modeling

Resolution:

Ensure that team members give adequate time on

MODELING

Discuss & Review all models thoroughly

Have experienced modeler as part of the team

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OOM Design: Creating Quality ClassesOOM Design: Creating Quality Classes

Creating Classes based on the analysis of Use-Case diagrams

will be significant step towards successful project design.

Creating Class diagram requires thinking at appropriate level of

abstraction ! Assigning appropriate responsibility to each Class requires

analytical thinking.

The Quality of Classes should be kept high from the Design

perspective. Functional IndependenceFunctional Independence

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OOM : design metricsOOM : design metrics

Main objectives :- to build highly cohesive classes

- to maintain loose coupling between those classes.

High-cohesion results in well-structured classes.

Loose coupling means more flexible, extensible software.

Applying this to the design and code helps determine whether

project goals have been achieved.


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CohesionCohesion

Classes contain certain data and exhibit certainbehavior.

Cohesive means that a certain class

performs a set ofclosely related actions.

A lack of cohesion means that a class is performingseveral unrelated tasks.

Lack of cohesion may never have an impact on theoverall functionality of a particular classor of theapplication itself

However, the application software will eventuallybecome unmanageable.


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Class Responsibility CollaborationClass Responsibility Collaboration

CRC cards are a brainstorming tool used in the design of object-oriented

software:

They are typically used when first determining which classes are needed and

how they will interact.

CRC cards are usually created from index cards on which are written:

The class name Its Superand Sub classes (if applicable)

The responsibilities of the class.

The names of other classes with which the class will collaborate to fulfill its

responsibilities.

Author

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Lethbridge/Laganire

2005

Chapter5: Modelling

with classes68

AllocatingAllocating responsibilitiesresponsibilities toto classesclasses

A responsibility is something that the system is required to do.

Each functional requirement must be attributed to one of the classes;

All the responsibilities of a given class should be clearly related.

If a class has too many responsibilities, considersplitting it into distinctclasses

If a class has no responsibilities attached to it, then it is probablyuseless

When a responsibility cannot be attributed to any of the existingclasses, then a new class should be created

To determine responsibilities

Perform use case analysis Look forverbsverbs and nounsnouns describing actionsactions in the system description


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Lethbridge/Laganire

2005

Chapter5: Modelling

with classes69

CategoriesCategories ofof responsibilitiesresponsibilities

Creating and initializing new instances

Loading to and saving from persistent storage

Destroying instances

Setting and getting the values of attributes

Computing numerical results

Adding and deleting links of associations

Copying, converting, transforming, transmitting or

outputting

Navigating and searching

Other specialized work


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OOSE forOOSE for

ATM Software : Case StudyATM Software : Case Study


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OOM for Software Project: ATM case studyOOM for Software Project: ATM case study

The software to be designed & developed will control a Simulated Automated

Teller Machine (ATM) having;

a magnetic stripe reader for reading an ATM card,

a customer console (keyboard and display) for interaction with

the customer,

a slot for depositing envelopes, a dispenser for cash (inmultiples of Rs.100/-),

a printer for printing customer receipts, and a key-operated

switch to allow an operator to start or stop the machine.

The ATM will communicate with the bank's computer over anappropriate communication link.

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Simulated ATM Case StudySimulated ATM Case Study


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The step-by-step progression towards the successful completion

of the project will require following;

Begin with the Requirements and User Interface.

The first task that must be performed in any project is clearly

understanding the requirements.

Then view the Use Cases and FurtherAnalysis.

Analysis is begun by identifying the use cases that follow from the

requirements, and detailing a flow of events for each.

Further analysis identifies the key classes that are suggested by

the use cases,

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The step-by-step progression will require following;

Begin with the Requirements and User Interface.

The first task that must be performed in any project is clearly

understanding the requirements.

Then view the Use Cases and FurtherAnalysis.

Analysis is begun by identifying the use cases that follow from the

requirements, and detailing a flow of events for each.

Further analysis identifies the key classes that are suggested bythe use cases,

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Requirement AnalysisRequirement Analysis&&

Use Case diagramUse Case diagram

forforATM SoftwareATM Software

ATM SoftwareATM Software


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It will service one customer at a time who will be required to enter a (PIN)-sent to the

bank for validation as part of each transaction.

The customer will then be able to perform one or more transactions.

ATM is able to provide the following services to the customer:

A customer must be able to make a cash withdrawal in multiples of Rs.100/. Approval

needed from the bank before cash is dispensed.

A customer must be able to make a deposit to any account linked to the card,

consisting of cash and/or checks in an envelope. The customer will enter the amount of the deposit into the ATM, subject to manual

verification when the envelope is removed from the machine by an operator. Approval

must be obtained from the bank before physically accepting the envelope.

A customer can make a transfer of money between any two A/C .

A customer must be able to make a balance inquiry of any account linked to the card.

A customer must be able to abort a transaction in progress by pressing the Cancel

key .

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What are the Actors & Use Cases in the given System?

There are followingActors;

Operator- who starts and closes the ATM machine.

Customer

Bank.

Operatorwill do following :-

System Start up

System shut down

Customerwill do following :-

Perform theATM sessionATM session involving;

Transaction in which

Withdrawal, Deposit, Transfer of money &

Inquiry related to Account

will be performed

BankBank will involved in the Transaction

ATM Software: Use Case diagramATM Software: Use Case diagram


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As per the given scenario the Use Cases can be identified in the given System;

With 03 Actors, following Use Cases will be in the system;

System Startup Use Case

System Shutdown Use Case

Session Use Case Transaction Use Case

Withdrawal Transaction Use Case

Deposit Transaction Use Case

Transfer Transaction Use Case

Inquiry Transaction Use Case

ATM : Transaction Use Case diagramATM : Transaction Use Case diagram


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As shown in the given scenario the Transaction Use Case will be under ATM Session use

case & needs to be further analyzed;

Transaction is an abstract generalization. Each specific concrete type of transaction

implements certain operations in the appropriate way. The flow of events will describes the

behavior common to all types of transaction. The flows of events for the individual types of

transaction (withdrawal, deposit, transfer, inquiry) give the features that are specific to that

type of transaction.

If the bank approves the transaction, any steps needed to complete the transaction (e.g.dispensing cash or accepting an envelope) will be performed, and then a receipt will be

printed. Then the customer will be asked whether he/she wishes to do another transaction.

If the bank reports that the customer's PIN is invalid, the Invalid PIN extension will be

performed and then an attempt will be made to continue the transaction. If the customer's

card is retained due to too many invalid PINs, the transaction will be aborted, and the

customer will not be offered the option of doing another. All messages to the bank and responses back are recorded in the ATM's log.

UU C di f th ATM tC di f th ATM t


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UseUse-- Case diagram of the ATM systemCase diagram of the ATM system

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U I t fU I t f


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User InterfaceUser Interface

User Interface for ATM Software will be similar to the ATM machine panel with

User friendly interface

Creating User Interface may be done either by MFC and Visual C++.

Sun had used a logical and object-oriented design for creating a GUI and

handling its events.

There are two APIs for creating GUI applications in Java: Swing andAWT(Abstract Windowing Toolkit).

When Java was first released in 1995, it contained a GUI API referred to as the

AWT.

This API contained classes like Frame to represent a typical window, Button to

represent buttons, Menu to represent a windows menu, and so on. The Swing API uses many of the AWT classes and interfaces.

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UI V i Alt tiUI V i Alt ti


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UI: Various AlternativesUI: Various Alternatives

AWT components are referred to as heavyweight components because their

implementation relies heavily on the underlying operating system.

The look and feel of AWT components depend on the platform the program is

running on. For example, an AWT button will look like a Windows button when

the program is run on a Windows platform. The same button will look like a

Macintosh button when the program is run on a Macintosh platform.

Swing is different from AWT in that Swing components are 100 percent Java,

thereby not relying on the native operating system or platform.

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We have studied the concepts of

Use Case Diagram

Class Diagram

To develop these STATIC Diagrams for ATM System.

Dynamic modeling diagrams

Develop dynamic diagrams for ATM Systems

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UseUse Case diagram: Analysis for ClassesCase diagram: Analysis for Classes


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UseUse-- Case diagram: Analysis for ClassesCase diagram: Analysis for Classes

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ATM : Analysis for ClassesATM : Analysis for Classes


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As initial in the Use Case diagram, now Classes needs to be analyzed;

A controller objectcontroller object representing theATMATM itself (managing the boundary objects as

listed )

Controller objectsController objects corresponding to use cases. (Note: class ATM can handle the

Startup and Shutdown use cases itself, so these do not give rise to separate objects

here.)

1)1) SessionSession

2)2) TransactionTransaction (abstract generalization, responsible for common features, withconcrete specializations responsible for type-specific portions)

Boundary objects representing the individual component parts of the ATM:

Operator panel.

Card reader.

Customer console, consisting of a display and keyboard. Network connection to the bank.

Cash dispenser.

Envelope acceptor. & Receipt printer.

Class AnalysisClass Analysis


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Class AnalysisClass Analysis

Controller objects corresponding to use cases; class ATMclass ATM can handle the

Startup and Shutdown use cases itself, so these do not give rise to separateobjects here.

Session

Transaction (abstract generalization, responsible forcommon features, with concrete specializations

responsible for type-specific portions)

An entity object representing the information encoded on the ATM card

inserted by customer.

An entity object representing the log of transactions maintained by the

machine.

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CRCCRC


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Using CRC cards to assign responsibilities to various classes for the tasks

required by the various use cases leads to the creation of the following cards.

Class ATMClass ATM

Controller objects corresponding to the variousController objects corresponding to the various use casesuse cases

Class SessionClass Session

Class TransactionClass Transaction

Class WithdrawalClass Withdrawal

Class DepositClass Deposit

Class TransferClass Transfer

Class InquiryClass Inquiry What about relations among these Classes?

Entity objects found necessary when assigning responsibilities to other object

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CRC for Class ATMCRC for Class ATM


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CRC for Class ATMCRC for Class ATM

Responsibilities CollaboratorsResponsibilities Collaborators Start up when

switch is turned on OperatorPanel

CashDispenser

NetworkToBank

Shut down when switch is turned off NetworkToBank

Start a new session when card is inserted by customer

CustomerConsoleSession

Provide access to component parts for sessions and transactions

CustomerConsoleSession

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ResponsibilitiesResponsibilities Collaborators Perform

session use case ATMCardReader

Card

CustomerConsole

Transaction

Update PIN value if customer has to re-enter it

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CRC: ClassCRC: Class CardReaderCardReader


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CRC: ClassCRC: Class CardReaderCardReader

Responsibilities CollaboratorsResponsibilities Collaborators

Tell ATM when card is inserted ATM

Read information from card Card Eject card

Retain card

Class Card

Responsibilities Collaborators

Represent information encoded on customer's ATM card

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Class DiagramClass Diagram


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Class DiagramClass Diagram

In the ATM system, one of the responsibilities of the ATM is to provide access

to its component parts for Session and Transaction objects; thus, Session andTransaction have associations to ATM, which in turn has associations to the

classes representing the individual component parts.

(Explicit "uses" links between Session and Transaction, on the one hand, and

the component parts of the ATM, on the other hand, have been omitted from

the diagram to avoid making it excessively cluttered.) The need for the various classes in the diagram was discovered at various

points in the design process.

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Class diagramClass diagram


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Some classes were discovered when doing analysis

Some classes were discovered when doing CRC cards

Message - used to represent a message to the bank.

Receipt - used to encapsulate information to be

printed on a receipt. Status - used to represent return value from message

to the bank.

Balances - used to record balance informationreturned by the bank

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Some Classes were discovered when doing detailed design or writing code

Money - used to represent money amounts, in

numerous places.

AccountInformation - contains names of varioustypes of accounts customer can choose from

That is, OO design is not a "waterfall" process - discoveries made when doing

detailed design and coding can impact overall system design.

To prevent the diagram from becoming overly large, only the name of each

class is shown - the attribute and behavior "compartments" are shown in the

detailed design, but are omitted here.

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ass agramass agram


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Modeling as UML :Static & DynamicModeling as UML :Static & Dynamic


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Modeling as UML :Static & DynamicModeling as UML :Static & Dynamic

94

Why dynamic modelingWhy dynamic modeling


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Why dynamic modelingWhy dynamic modeling

As the software system continuously changes ( in states, activities, and

collaborations) during life time, therefore it is needful to model it and following

are grouped in the dynamic modeling diagrams of UML;

StatesStates

SequencesSequences

CollaborationsCollaborations

ActivitiesActivities

These diagram shows how objects interact dynamically, during execution time of

the system.

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dynamic modeling diagramsdynamic modeling diagrams


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dynamic modeling diagramsdynamic modeling diagrams

There are following four diagrams, who represent the behavioral view of the system and as

behavior is a dynamic phenomenon, the diagrams are also categorized as Dynamic modeling

diagrams

1. State diagrams describes different states an object can have during its life cycle, behavior

in the states, events that can change states

2. Sequence diagrams describes how objects interact and communicate with each other with

the focus on time

3. Collaboration diagrams also describes how objects interact, but the focus is on space

4. Activity diagrams another way to show interaction but the focus is on work

State chart diagramsState chart diagrams


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State chart diagramsState chart diagrams

Objects have behaviorsbehaviors (methods) and statestate (attributes)(attributes).

The state of an object depends on its current activity or condition.

A state chart diagram shows the possible states of the object and

the transitions that cause a change in state.

Captures life cycle of objects, subsystems and systems. Tells us the states that an object can have and what events can

change the states.

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Activity diagramsActivity diagrams


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The activity diagram is possibly one modeling element which was not present in

any of the predecessors of UML. No such diagrams were present either in theworks of Booch, Jacobson, or Rumbaugh.

The activity diagram focuses on representing activities or chunks of processing

which may or may not correspond to the methods of classes.

An activity is a state with an internal action and one or more outgoing

transitions which automatically follow the termination of the internal activity.

If an activity has more than one outgoing transitions, then these must be

identified through conditions.

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Activity DiagramsActivity Diagrams


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Activity DiagramsActivity Diagrams

An interesting feature of the activity diagrams is the swim lanes.

Swim lanes enable you to group activities based on who is performing them.

Thus swim lanes subdivide activities based on the responsibilities of some

components.

The activities in a swim lane can be assigned to some model elements, e.g.

classes orsome component, etc. Activity diagrams are normally employed in business process modelingbusiness process modeling. This is

carried out during the initial stages of requirements analysis and specification.

Activity diagrams can be very useful to understand complex processing

activities involving many components. Later these diagrams can be used to

develop interaction diagrams which help to allocate activities (responsibilities)to classes.

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Activity diagram vs. State chart diagramActivity diagram vs. State chart diagram


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Activity diagram vs. State chart diagramActivity diagram vs. State chart diagram

Both activity and state chart diagrams model the dynamic behavior of the

system. Activity diagram is essentially a flowchart showing flow of control fromactivity to activity. A state chart diagram shows a state machine emphasizing

the flow of control from state to state.

An activity diagram is a special case of a state chart diagram in which all or

most of the states are activity states and all or most of the transitions are

triggered by completion of activities in the source state (An activity is anongoing non-atomic execution within a state machine).

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Activity diagram Vs. State chart diagramActivity diagram Vs. State chart diagram


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Activity diagram Vs. State chart diagramActivity diagram Vs. State chart diagram

101

Activity diagramsActivity diagrams may stand alone to visualize, specify, anddocument the dynamics of a society of objects or they may be used to

model the flow of control of an operation.

State chart diagramsState chart diagrams may be attached

to classes, use cases, or entire systems in order to visualize, specify,and document the dynamics of an individual object.

State Chart diagramState Chart diagram


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State Chart diagramState Chart diagram

The basic elements of the state chart diagram are as follows: Initial state. This

is represented as a filled circle.

Final stateFinal state. This is represented by a filled circle inside a larger circle.

StateState. These are represented by rectangles with rounded corners.

TransitionTransition. A transition is shown as an arrow between two states. Normally, the

name of the event which causes the transition is places along side the arrow. Aguard to the transition can also be assigned. A guard is a Boolean logic

condition. The transition can take place only if the grade evaluates to true.

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StatechartStatechart diagramdiagram


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ObjectsObjects have behaviors and state.

The state of an object depends on its current activity or condition.

A statechart diagram shows the possible states of the object and the

transitions that cause a change in state.

Let us consider another similar banking application and model the Login partLogin part

of an online banking system.of an online banking system.

Logging in consists of entering a valid social security numberand personal id

number, then submitting the information for validation.

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Logging in Banking systemLogging in Banking system


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Logging in Banking systemLogging in Banking system

Logging inLogging in can be factored into four non-overlapping states:

I. Getting SSN,

II. Getting PIN,

III. Validating, and

IV. Rejecting.

From each state comes a complete set of transitions that determine the

subsequent state.

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StatechartStatechart diagram for Banking Logging in Systemdiagram for Banking Logging in System


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105

States are rounded rectangles. Transitions are arrows from one state toanother.Events or conditions that trigger transitions are written beside thearrows. Our diagram has twotwo selfself--transitiontransition, one on Getting SSN and

anotheron Getting PIN.

Logging in systemLogging in system


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gg g ygg g y

The initial state (black circle) is a dummy to start the action. Final states are

also dummy states that terminate the action.

The action that occurs as a result of an event or condition is expressed in the

form /action.

While in its Validating state, the object does not wait for an outside event to

trigger a transition. Instead, it performs an activity. The result of that activity

determines its subsequent state.

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y gy g

An activity diagram is essentially a fancy flowchart. Activity diagrams and

statechart diagrams are related. While a statechart diagram focuses attentionon an object undergoing a process (or on a process as an object), an activity

diagram focuses on the flow of activities involved in a single process. The

activity diagram shows the how those activities depend on one another.

For our example, we used the following process.

"Withdraw money from a bank account through an ATM."Withdraw money from a bank account through an ATM."

The three involved classes (people, etc.) of the activity are Customer, ATM,

and Bank.

The process begins at the black start circle at the topblack start circle at the top and ends at the

concentric white/black stop circlesconcentric white/black stop circles at the bottom.

The activities are rounded rectangles.

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Activity diagramActivity diagram


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Interaction DiagramsInteraction Diagrams


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Interaction diagrams are models that describe how group of objects collaboratecollaborate

to realize some behavior.

Typically, each interaction diagram realizes the behavior of a single use case. An interaction diagraminteraction diagram shows a number of example objects and the messages

that are passed between the objects within the use case.

There are two kindstwo kinds of interaction diagrams:

sequence diagrams and collaboration diagrams. These two diagrams are equivalent in the sense that any one diagram can be

derived automatically from the other.

These two actually portray different perspectives of behavior of the system and

different types of inferences can be drawn from them. The interaction diagrams

can be considered as a major tool in the design methodology.

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Sequence DiagramSequence Diagram


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q gq g

A sequence diagram is an interaction diagram that details how operations are

carried out -- what messages are sent and when.

Sequence diagrams are organized according to timetime.

Focus is on message sequences.

Sequence diagrams have two axestwo axes:

VerticalVertical timeHorizontalHorizontal set of objects.

The timetime progresses as you go down the page.

The objectsobjects involved in the operation are listed from left to rightleft to right according to

when they take part in the message sequence.

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Sequence diagramSequence diagram


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q gq g

Each message in Sequence diagram is labeled with the message name.

Some control information can also be included. Two types of control

information are particularly valuable:-

A condition (e.g. [invalid]) indicates that a message is sent, only if the conditionis true.

An iteration markeriteration marker shows the message is sent many times to multiple receiver

objects as would happen when a collection or the elements of an array are

being iterated.

The basis of the iteration can also be indicated .

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Collaboration DiagramCollaboration Diagram


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A collaboration diagram shows both structural and behavioral aspectsstructural and behavioral aspects explicitly.

This is unlikunlike a sequence diagram which shows only the behavioral aspectsbehavioral aspects. The structural aspect of a collaboration diagram consists of objects and the

links existing between them. In this diagram, an object is also called a

collaborator.collaborator.

The behavioral aspect is described by the set of messages exchanged amongset of messages exchanged among

the different collaborators.the different collaborators. The linklink between objects is shown as a solid linesolid lineand can be used to send messages between two objects.

The messagemessage is shown as a labeled arrow placed near the link. Messages are

prefixed with sequence numberssequence numbers because they are only way to describe the

relative sequencing of the messages in this diagram.

The use of the collaboration diagrams in our development process would be tohelp us to determine which classes are associated with which other classes.

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Collaboration diagramsCollaboration diagrams


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Focus is on interactions between objects with the emphasis on space

Note that the emphasis in sequence diagrams was on time

Collaboration diagrams show the objects and their links to each other

A link is an instance of an association.

Collaboration diagrams are also interaction diagrams. They convey the same information as

sequence diagrams, but they focus on object roles instead of the times that messages are

sent.

In a sequence diagram, object roles are the vertices and messages are the connecting links.

Collaboration diagramCollaboration diagram


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117

The object-role rectangles are labeled with eitherclass or object

names (or both).Class names are preceded by colons ( : ).Each message in a collaboration diagram has a sequencenumber. The top-level message is numbered 1. Messages at thesame level (sent during the same call) have the same decimalprefix but suffixes of 1, 2, etc. according to when they occur.

LinksLinks


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A link is a connection between two objects

Role names of the objects can be shown at the end of the links

Qualifiers can also be shown on the links

Stereotypes may be attached to the roles of the objects

Standard stereotypes are: global, local, parameter, self, vote, broadcast

Types of linksTypes of links


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Global - corresponding instance is visible because it is global in

scope Local - corresponding instance is visible because it is local in

scope

Parameter visible because it is a parameter in an operation

Self specifies that the object can send message to itself Vote constrains a collection of return messages such that the

return value is selected through a majority vote

Broadcast specifies that the set of messages are not invoked in

a certain order

PolymorphismPolymorphism


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Ex. Bird, Person and Fish

are child classes ofAnimal. Each subclass overrides

the move() method in itsown way

Animal [] A = newnew Animal[3];

A[0] = new Bird();A[1] = new Person();

A[2] = new Fish();

for (int i = 0; i < A.length; i++)

A[i].move();

move()

move()

move()

References are all the same, butobjects are not

Method invoked is thatassociated with the OBJECT, NOT

with the referencereference


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InheritanceInheritance -- related Terminologyrelated Terminology


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21/09/201002:10:45 Marc Conrad -

University of Luton

122

Derived class orsubclass orchild class. A class which inherits some of its attributes and methods

from another class.

Base class orsuperclass orparent class.

A class from which another class inherits.

Ancestor.

A classs ancestors are those from which its own

superclasses inherit.

Descendant.

A classs descendants are those which inherit from its

subclasses.

Inheritance vs. AggregationInheritance vs. Aggregation


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21/09/201002:10:45 Marc Conrad -

University of Luton

123

Inheritance means that one class inherits the

characteristics of another class.

This is also called a is a relationship:

Aggregation describes a has a relationship. One object

is a part of another object.

A caris a vehicle

A carhas wheels

A student is a person

A person has legs

Inheritance and is aInheritance and is a


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We can understand this the is a idea A subclass object is a superclass object

However, some extra instance variables and methods mayhave been added and some other methods may have beenchanged

Note that is a is a one way operation

Subclass is a superclass (specific "is a" general)

With modifications / additions

Superclass is NOT a subclass (general not "is a" specific Missing some properties

Inheritance and is aInheritance and is a


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Bird, Human and Fish are all Animals

However, an Animal is not necessarily a Bird, Human orFish

Animal

Bird Human Fish

is ais a

is a


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CompositionComposition


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object composition is a way to combine simple objects or data types into more

complex ones. Compositions are a critical building block of many basic data structures,

including the tagged union, the linked list, and the binary tree, as well as the

object used in object-oriented programming.

Composited (composed) objects are often referred to as having a "has a"

relationship.

A real-world example of composition may be seen in an automobile: the objects

wheel, steering wheel, seat, gearbox and engine may have no functionality by

themselves, but an object called automobile containing all of those objects

would serve a higher function, greater than the sum of its parts.

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When, in a language, objects are typed, types can often be divided into

composite and noncomposite types, and composition can be regarded as arelationship between types: an object of a composite type (e.g. car) "has an"

object of a simpler type (e.g. wheel).

Composition must be distinguished from subtypingsubtyping which is the process of

adding detail to a general data type to create a more specific data type. For

instance, cars may be a specific type of vehicle: caris a vehicle. Subtyping doesn't describe a relationship between different objects, but

instead, says that objects of a type are simultaneously objects of another type.

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In programming languages, composite objects are usually expressed by means

of references from one object to another; depending on the language, suchreferences may be known as fields, members, properties or attributes, and the

resulting composition as a structure, storage record, tuple, user-defined type

(UDT), or composite type.

Fields are given a unique name so that each one can be distinguished from

the others. However, having such references doesn't necessarily mean that an object is a

composite.

It is only called composite if the objects it refers to are really its parts, i.e. have

no independent existence. For details, see the aggregation section below.

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AggregationAggregation


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Aggregation differs from ordinary composition in that it does not imply

ownership. In composition, when the owning object is destroyed, so are thecontained objects. In aggregation, this is not necessarily true.

For example, a university owns various departments (e.g., chemistry), and

each department has a number of professors. If the university closes, the

departments will no longer exist, but the professors in those departments will

continue to exist. Therefore, a University can be seen as a composition ofdepartments, whereas departments have an aggregation of professors. In

addition, a Professor could work in more than one department, but a

department could not be part of more than one university.

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UML notationUML notation


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In UML, composition is depicted as a filled diamond and a solid line. It always

implies a multiplicity of 1 or 0..1, as no more than one object at a time can havelifetime responsibility for another object.

The more general form, aggregation, is depicted as an unfilled diamond and a

solid line. The image below shows both composition and aggregation.

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Composition & AggregationComposition & Aggregation


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The C++ code below shows what the source code is likely to look like.The C++ code below shows what the source code is likely to look like.

//// CompositionComposition

class Car { private: Carburetor* itsCarb; public: Car() {itsCarb=new

Carburetor();} virtual ~Car() {delete itsCarb;} };

// Aggregation

class Pond { private: vector itsDucks; };132

Example: OOM designExample: OOM design

As we have seen in the Employee Compute pay example the Salary and


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As we have seen in the Employee Compute pay example, the Salary and

Hourly classes are repeating code. Salary and hourly employees are still

employees, and there is a lot of information in common between the two. Although Salary and Hourly employees are different types, they are not

entirely different. Which is seen by the repetition of fields and methods in

these two classes.

The Salary and Hourly classes demonstrate the need forinheritance.

Using inheritance will improve this design considerably, not only to avoid

repeating code, but also to create a program design that allows for better

maintenance and code changes later.

Therefore, writing two separate classes for the two different types of employees is

not yet a satisfactory solution.

Design in OOSE is definitely an issue.

Two ClassesTwo Classes

public class Salarypublic class Hourly

{


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{

public String name;

public String address;

public int SSN;

public int number;

public float salary;

public void mailCheck(){

System.out.println(Mailing a check to +

name

+ + address);

}

public float computePay()

{

return (float) salary/52.0;

}

{

public String name;

public String address;public int SSN;

public int number;

public float hourlyRate;

public float hoursWorked

public void mailCheck()

{

System.out.println(Mailing a check to +

name + + address);

}

public float computePay()

{ return (float) hoursWorked * hourlyRate;

}

}134

OOMOOM


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A better design for the Salary and Hourly classes is to take their common

elements and put them in a parent class, leaving the unique elements in thechild classes.

For example, the mailCheck() method could appear in the Employee parent

class, and the computePay() method could appear in each of the child classes.

The assumption is that the process of mailing a check is the same for all

employees, but computing their pay is directly affected by how they are paid.

Employees do not share a common computePay() method. By placing

computePay() in each child class, the method will be written twice.

This is not repeating code, though, because computePay() in Salary is quite

different than computePay() in Hourly.

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Example: OOM designExample: OOM designThis benefit is difficult to achieve with procedural programming and also with poorly designed OOP


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p p g g p y g

applications.

To avoid these situations, constantly test yourOOP design against these simple rules:

An object has an attribute, and an object does a behavior.An object has an attribute, and an object does a behavior.

In our employee example, if it is not true that an employee has a salary, an Employee class should not

have a salary field, and we should redesign our program.

None of the existing code needs to be touched.

With OOPS Characteristics - inheritance, all of these issues are avoided.

The common features of employees appear in a parent class. Each different type of employee is

represented by a child class.

When a new type of employee such as a contractorcomes along, a new child class is written that

extends the parent class.

Using inheritance will improve this design considerably, not only to avoid repeating

code, but also to create a program design that allows for better maintenance andcode changes later.

TheThe is a Relationshipis a Relationship

Th i l ti hi i i l b t f l l f t ti if i h it


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The is a relationship is a simple but powerful rule for testing if your inheritance

is a good design.

Whenever you use inheritance, you should be able to say that a childchild is aparentparent.

If this statement is true, your inheritance is likely a good design.

For example, it is true that a salaried employeea salaried employee is anis an employee.employee.

Similarly, an hourly employeehourly employee is anis an employee;employee; therefore, it is reasonable thatthe Salary and Hourly classes extend the Employee class.

Lets look at an example where inheritance is not a good idea. Suppose that

you have a Date class that represents a calendar date, and you want to use

that class to keep track of the date when an employee was hired.

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Inheritance ?Inheritance ?


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Because inheritance has so many benefits, you decide to have the Employee

class extend the Date class. When you instantiate an Employee object, you will also get a Date object for

storing the employees hire date; however, is it true that an employee is a date?

The is a relationship clearly fails here. Although the result might work for us, an

Employee class inheriting from a Date class is not a good design and should

not be used. The solution to the improperuse of inheritance with the Employee and Date

classes is to realize that an employee has a hire date, not that an employee is

a hire date. If an object has an attribute, the attribute should be a field in the

class.

The Employee class should add a field of type Date to represent the hire dateof an employee, as opposed to extending the Date class.

138

Object Oriented MethodologyObject Oriented Methodology


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Objects & Classes in JavaObjects & Classes in Java

Writing a Class in JavaWriting a Class in Java .

OOM design issuesOOM design issues

OOM Characteristics:

Inheritance: When to use / not to use ? Implementing Inheritance: Instantiating Child objects

Types of Inheritance

ObjectObject Class : Over riding ?

Super keyword & Final methods

Modeling in OOM way Modeling in OOM way

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InheritanceInheritance


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A child class has access to the fields and methods in the parent class,

depending on the access specifier, The computePaycomputePay() method() method of the Salary class displays the name of the

employee being paid, but there is no nameno name field in the salary class.

The name field is in Employee, the parent of Salary. In this example, becausebecause

name isname is publicpublic, Salary has acces to it and can use it at any point in the Salary

class. (What will happen if it is Private?) Notice that the Hourly class print

Date post:	10-Apr-2018
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OOSE3 OOSE in Real World and Industry

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