SoftEng Process Models

8/6/2019 SoftEng Process Models

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NEU CS424 SoftwareEngineering

Software Engineering

The application of systematic,

disciplined, quantifiable approach to the

development, operation, and

maintenance of software, that is the

application of engineering to software

- IEEE


2/22


MANAGEMENT: Managers

and leaders should promote an

ethical approach to the

management of software

development PROFESSION: Advance the

integrity and reputation of the

profession

COLLEAGUES: Be fair and

supportive of colleagues

SELF: Participate in lifelonglearning, promote ethical

approach to the profession

PUBLIC: Act consistently with

the public interest

CLIENT AND EMPLOYER: Act

in the best interest of client and

employer, consistent with thepublic interest

PRODUCT: Ensure product

meets highest professional

standards

JUDGMENT: Maintain integrity

and independence inprofessional judgment

ACM/IEEE Code of Ethics(available at http://www.acm.org/serving/se/code.htm)


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Software != CodeSource code is asubsetsoftware project

Requirements and specification

Design documents

Test suites, test plans

InterfacesDocumentation

Software is notwhat we think it is


4/22


Large Software != Lots of Code

Large software brings up several issues of scale: Total comprehensibility must be forfeited

Solo programming becomes impossible

Communication becomes an essential challenge

Changing requirements are an everyday reality

Lifetime is measured in years or decades

People dont know what they want

Large software is notwhat we think it is


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Software as a Product

Software is expensive!

The major cost is your salary!

Every software project has a trade-off between:

Functionality

Resources (cost)

Timeliness


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Client (a.k.a. Customer)

# The client provides resources and expects some product

in return.

# Client satisfaction is the primary measurement of

success.

Question: Who is the client for Microsoft Excel?


7/22


Variety of Software Products

Examples

Real time: air traffic control

Embedded systems: digital camera, GPS

Data processing: telephone billing, pensionsInformation systems: web sites, digital libraries

Sensors: weather data

System software: operating systems, compilers

Communications: routers, mobile telephonesOffices: word processing, video conferences

Scientific: simulations, weather forecasting

Graphical: film making, design

etc., etc., etc., ....


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General characteristics

Usability

Maintainability

DependabilityEfficiency

Good software products require good programming,

but ...

Programming quality is the means to the end, not the

end itself.

Characteristics of All Software

Products


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Usefulness

Modularization

Reliability Robustness

Usability

Efficiency

Flexibility

Good internal documentation Good external documentation

Software Qualities


10/22


Correctness

- No errors

Usefulness- Does what we want to do

Minimal production effort

minimal cost

minimal time maximum profit

Minimal maintenance effort

Ideal Goals of Software

Engineering


11/22


Categories of Product

Categories of client and software product:

# Generic (e.g., Microsoft Excel)

# Bespoke (customized) (e.g., IRS internal

system)

Many systems are customized versions of genericpackages (e.g., Cornell's payroll system)


12/22


Variety of Software Products

Software products are very varied

--> Client requirements are very different

--> There is no standard process for software engineering

--> There is no best language, operating system, platform,

database system, development environment, etc.

A skilled software developer knows about a wide variety ofapproaches, methods, tools. The craft of software engineering

is to select appropriate methods for each project and apply them

effectively.


13/22


Professional Responsibility

Organizations put trust in software developers:

Competence: Software that does not work effectively can

destroy an organization.

Confidentiality: Software developers and systems

administrators may have access to highly confidential

information (e.g., trade secrets, personal data).

Legal environment: Software exists in a complex legalenvironment (e.g., intellectual property, obscenity).

Acceptable use and misuse: Computer abuse can paralyze an

organization (e.g., the Internet worm).


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Requirements Analysis & Specification

Conceptual/System Design

Detailed/Program Design

Implementation/Coding

Unit & Integration Testing

System Testing

System Delivery

Maintenance

Software Development Stages


15/22


Waterfall Model

V Model

Prototyping Model

Operational Specification Model

Phased Development Model Spiral Model

Software Lifecycle Models


16/22


Waterfall ModelREQUIREMENT

NALYSIS

SYSTEM

DESI N

PROGRAM

DESIGN

CODING

UNIT & INTE-

GRATION TESTING

SYSTEM

TESTING

ACCEPTANCE

TESTINGOPERATION

& MAINTENANCE[Pfleeger 98]


17/22


V ModelREQUIREMENTS

ANALYSIS

SYSTEMDESIGN

PROGRAM

DESIGN

CODING

UNIT & INTE-

GRATION TESTING

SYSTEM

TESTING

ACCEPTANCE

TESTING

OPERATION

& MAINTENANCE

Veri y design

Validate requirements

[Pfleeger 98]


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Prototyping Model

Listen toCustomer

Customer

Test-drives

Mock-up

Build/ReviseMock-Up

[Pressman 97]


19/22


Prototyping ModelLIST OF

REVISIONS

LIST OF

REVISIONS

LIST OF

REVISIONS

PROTOTYPE

REQUIREMENTS

PROTOTYPE

DESIGN

PROTOTYPE

SYSTEMTEST

DELIVERED

SYSTEMSYSTEM

REQUIREMENTS

(sometimes informal

or incomplete)

revise

prototype

user/

customer

review

[Pfleeger 98]


20/22


Operational Specification

Model

TEST

DELIVEREDSYSTEM

Execute and

Revise

OPERATIONAL

SPECI ICATION

(problem-oriented)

TRANSFORMED

SPECIFICATION

(implementation-

oriented)

SYSTEM

REQUIREMENTS

(sometimes informal

or incomplete)

[Pfleeger 98]


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Phased Development ModelDevelopment systems

Production systems

DEVELOPERS

USERS

Build Release 1

Use Release 1

Build Release 2

Use Release 2

Build Release 3

Use Release 3

Time

[Pfleeger 98]


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Boehms Spiral Model

PLAN DEVELOP AND TEST

DETERMINE GOALS,ALTERNATIVES,CONSTRAINTS

EVALUATE ALTERNATIVESAND RISKS

Requirements,

life-cycle plan

Budget1

Risk analysis1

Risk analysis 2

Risk analysis3

Risk analysis 4

Budget2

Budget3

Budget 4 Prototype1

Proto -

type 2

Proto-

type 3

Proto-

type 4

Concept of

operationDetailed

design

Code

Unit test

System

testAcceptance

test

Implementation

plan

[Pfleeger 98]

start

Documents

SoftEng Process Models