19 . System Analysis and Development

19. System Analysis and DevelopmentRev: Feb, 2013

Euiho (David) Suh, Ph.D.

POSTECH Strategic Management of Information and Technology Laboratory(POSMIT: http://posmit.postech.ac.kr)

Dept. of Industrial & Management EngineeringPOSTECH

Contents1 System Analysis

(1) Basic Concepts

(2) Modeling

2 System Development

(1) Systems Development Life Cycle (SDLC)

(2) Rapid Application Development (RAD)

(3) Prototyping

3 Case Study

3

System Analysis (SA)

■ Definition of SA– To model the real-world system so that it can be understood

■ Goals of SA– To fully specify the problem and application domain without introducing a bias to any

particular implementation

■ Benefits of SA– It clarifies the requirements of customer (end-user)– It provides a basis for agreement between customer and the developer – It becomes the framework for later design and implementation

1. System Analysis(1) Basic concepts

4

Overview of Analysis1. System Analysis(1) Basic concepts

Users

Developer

Manager

GenerateRequests

User interview

Domain knowledge

Real-world experience

BuildModel

ProblemStatement

Data ModelFunctional ModelBehavioral Model

Analysis

Design

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Problem Statement

■ Consist of requirements statement and design & implementation policy

■ Requirement statements– Problem scope

– Application Context

– Assumptions

– Performance Needs

■ Design & implementation policy– General approach

– Algorithms

– Data Structures

– Architecture

1. System Analysis(1) Basic concepts

6

Data Modeling (1/2)

■ Data model answers following specific questions– What are the primary data objects to be processed by the system?

– What is the composition of each data objects and what attributes describe the object?

– Where do the objects currently reside?

– What are the relationships between each object and other objects?

– What is the relationship between the objects and the processes that transform them?

■ Data modeling methods– ERD (Entity Relationship Diagram)

– DD (Data Dictionary)

– OM (Object Modeling): object-oriented modeling method

1. System Analysis(2) Modeling

7

Data Modeling (2/2)

■ ERD


ManufacturerManufacturer BuildsBuilds CarCar

DealershipDealershipShipperShipper

LicensesLicenses StocksStocksContractsContracts

Entity

Relationship

Cardinality

8

Functional Modeling (1/2)

■ Functional model shows – How values are computed, without regard for sequencing, decision, or object structure – Which values depend on which other values and the functions that relate them

■ Steps for constructing a functional model– Identify input and output values– Show functional dependencies (using DFD or IDEF0)– Describe functions– Identify constraints

■ Identify input and output values– E.g.) Input and output values

for ATM system


Cashcard

Cashcard

UserUser

ATMATM

bank code, card code

PasswordTransaction kind,Account type,amount cash.,

receipt.,messages System boundary

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Functional Modeling (2/2)

■ Describing functions– E.g.) Function description for update account function


Update account(account, amount, transaction-kind) -> cash, receipt, message If the account on a withdrawal exceeds the current account balance,

reject the transaction and dispense no cash If the account on a withdrawal does not exceed the current account balance

debit the account and dispense the amount requested If the transaction is a deposit

credit the account and dispense no cash If the transaction is a status request

dispense no cash In any case,

the receipt shows ATM number, date, time, account number,transaction-kind, amount transacted(if any), and new balance

10

Behavioral Modeling (1/4)

■ Behavioral model– Shows the time-dependent behavior of the system and object in it– Begins by looking for events (externally-visible stimuli & responses)– Is insignificant for a purely static data repository, such as a DB– Is important for interactive system

■ Steps for constructing a Behavioral model– Prepare scenarios of typical interaction sequences– Identify events between objects– Prepare an event trace for each scenario– Build a state diagram


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■ Prepare scenarios– E.g.) Normal ATM scenario

■ Identify Events– Examine scenario to identify all external events: Events include all signals, inputs, de-

cisions, interrupts, transitions, and actions to or from users or external devices

■ Prepare an event trace– E.g.) Event trace for ATM scenario (next slide)

■ Build a state diagram– E.g.) State diagram for ATM (next slide)


The ATM asks the user to insert a card; the user insert a cash card.The ATM accepts the card and reads its serial numberThe ATM requests the password : the user enters “1234”The ATM verifies the serial number and password with the consortium; the consortium checks it with bank “39” and notifies the ATM of acceptanceThe ATM asks the user to select the kind of transaction ; the user select withdrawalThe ATM asks for the amount of cash ; the user enters $100The ATM asks the consortium to process the transaction ; consortium passes the request to the bankThe ATM dispenses cash and asks the user to take it; the user takes the cashThe ATM asks whether the user wants to continue; the user indicates noThe ATM prints a receipt, ejects the card, and asks the user to take them; the user takes the receipt and the cardThe ATM asks a user to insert a card

12


■ Event trace


User ATM Consortium Bank

Insert card

Request passwordEnter password

Verify accountVerify card

Bank account OKAccount OK

Request kind

Enter kind

Request amount

Enter amountProcess transaction Process bank

succeed

13


■ State diagram


Main screenDo: display main

screen

Insert card[readable]

Insert card[unreadable]

Do: request password

UnreadableDo: UnreadableCard message

Enter password Do: verify account

Account OK

Do: request kind

Do: verify account

Cancel Enter Kind

CancelDo: canceled

message Cancel

Enter amount

Do: process transaction

Card ejectedDo: eject card;

Request take card

Takecard

Cancel

Do: dispense cash;request take cash

Do: request continuation

TransactionsucceedTake cash

Badaccount

Do: bad account message;Finish

Do: print receipt

Terminatecancel

14

Systems Development Life Cycle (SDLC)

■ Definition– The overall process of developing information systems through a multi step process

from investigation of initial requirements through analysis, design, implementation and maintenance <Russell Kay, Computer World>

■ Types of SDLC– Waterfall• Major methodology of SDLC

– Fountain– Spiral

■ Outputs from one step → Inputs to next

■ Often referred to as the “waterfall” model(The oldest one - early 1970s)

2. System Development(1) SDLC - Introduction to SDLC

15

5 Phases of Waterfall Development Method

Systems AnalysisSystems Designs

2. System Development(1) SDLC - Waterfall Development Method

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Phase 1: Investigation

■ Initialization– Management planning, Users’ needs & opportunities

■ Formal definition– Objective, motivation, scope, boundaries, constraints, strategy– Verifying a problem or deficiency which really exists, or passing judgment on the new

requirement

■ Feasibilities studies

Technical Fea-sibility

• Availability of computing hardware and software to do a particular jobManagers’ concerns about the absence of technology in many cases

Economic Feasibility

• Ability of a system to pay for itself in monetary termsNo unprofitable spendinge.g.) Cost-benefit Analysis, Break-even Analysis, Payback Analysis, NPV

Operational Feasibility

• Ability of the people working within a system to do their jobs in a pre-scribed manner

e.g.) Ability of Users and Participants & Attitudes of Users and Participants

Organiza-tional Feasibil-

ity

• How well a proposed e-commerce system helps the company’s plans for developing Web-based sales, marketing, and financial system


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Phase 2: Analysis

■ What a system should do to meet the needs of users

■ Determine requirements– Study current system– Structure requirements and eliminate redundancies

■ Requirement Analysis– Functional requirements– Performance requirements

■ Generate alternative designs

■ Compare alternatives

■ Recommend best alternative


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■ How the system will accomplish the objective

■ User interface Design– Screen– Form– Report– Dialog Design

■ Data Design– Data Element structure Design

■ Process Design– Program and Procedure Design

Phase 3: Design2. System Development

(1) SDLC - Waterfall Development Method

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Phase 4: Implementation

■ Evaluating Hardware, Software, and Services– Scoring evaluation system:

Used when there are several competing proposals for a hardware or software acquisi-tion

■ Software Development or Modification

■ Documentation – Major mechanism of communication during development process

■ Data Conversion– Correcting incorrect data– Filtering unwanted data– Consolidating data from several data warehouses.

■ Testing– Testing & Debugging the Software

■ Training


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Phase 4: Implementation

■ Conversion

Running old & new systems for awhile to check validity

Safe

Parallel Strategy

Installed in one part of organi-zation at a time

Learning and adapting

Pilot Strategy

Changing one function at a time in large system

e.g. order entry

Phased Strategy

Starting using entire system

Dangerous if errors exist

Plunge Strategy


21

Phase 5: Maintenance

■ Modification– Modifying established system due to changes in the system

for potential problems or necessary change

■ Correcting errors

■ Feedback

<Martin, “Managing Information Technology” p.395>


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Pros and Cons of SDLC

■ Advantages– Highly structured, systematic process – Thorough requirements definition– Clear milestone with business management sign-offs

■ Disadvantages– Not accounting well for evolving requirements during project– Time-consuming (and costly) process

2. System Development(1) SDLC - Pros and Cons of SDLC

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Rapid Application Development (RAD)

■ Definition– Rapid Application Design– A system development methodology created to radically decrease the time needed to

design and implement information systems<James Martin, “RAD,

CIRCA”>

■ Motivation of Rapid Application Development (RAD)– Limitation of SDLC– Pressures for businesses to speed up– Shorter development lifecycles– Competition in changing global environment

“Why wait 3 years to develop systemslikely to be obsolete upon completion?”

RAD methodology was born!

2. System Development(2) RAD

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The 4 Essentials of RAD (1/2)

■ Management– Executives, Support for the RAD

■ People– Participation in JAD type– Specialized team for RAD: SWAT(“Skilled With Advanced Tools”)

Joint application design (JAD) Group Decision Support System Users, Managers and Analysts work together for several days System requirements are reviewed Structured meetings

■ Methodologies– RAD life cycle: Users play key roles

■ Tools– Fourth-generation languages and CASE tools that facilitate prototyping and code genera-

tion

Computer-Aided Software Engineering (CASE) Any software tool to transfer some of the systems development workload

from the human developer to the computerby automating one or more steps of a software development methodology


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RAD Life Cycle

JAD session to develop basis de-sign

CASE tool is used

Delivery of new system to users

JRP(Joint Requirement Planning) workshopsto agree requirements, overall planning

Executives, managers, and users determine require-ments

Generate code End users validate design


26

Prototyping

■ Definition– The overall process of developing IS, which enables creation of system (or part of sys-

tem) more quickly, then revising after users have tried it<Martin, “Managing Information

Technology”>

■ Selected features:Only some essential features included in prototype, more added later

2. System Development(3) Prototyping

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Prototyping Life Cycle

Prototype cycle


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Pro and Cons of Prototyping

■ Advantages– Improved communications between the developer and user– A more active role of users in system development– Less time and effort of information specialists and user in developing the system– Much easier implementation due to the user’s understanding about what to expect

■ Disadvantages– Lack of security and control features in end prototype– Possibility that prototyping may not undergo as rigorous testing– Possibility of less complete final documentation– Bigger difficulty to manage user expectations


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3 Types of System Development

SDLC

RAD

Prototyp-ing

SPEED

STABILITY

Large and complex sys-tem

Hybrid type of SDLC and Prototyp-ing

When requirements are hard to de-fine

Trade-off


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Reference

■ O’Brien & Marakas, “Introduction to Information Systems – Sixteenth Edition”, McGraw – Hill, Chapter 11

■ O’Brien & Marakas, “Introduction to Information Systems – Sixteenth Edition”, McGraw – Hill, Chapter 12

■ Hyungjong Roh, “System Development Methods (PPT slide)”

http://mis.postech.ac.kr/class/IMEN381_MIS/Textbook%20IIS%2016th/chap011.ppt











http://mis.postech.ac.kr/class/IMEN381_MIS/references/System_Development_Methods.ppt



19 . System Analysis and Development

Documents

functional modeling

realworld system

atm system

data modeling 22erd1

account type

primary data objects

data model answers

update account function