8[1]. Software Engineering Concepts

8/8/2019 8[1]. Software Engineering Concepts

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Summer 2009

Lesson - 8

Software Engineering

Concepts

CSE 101


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What is software?

Computer programs andassociated documentation

Software products may be developed for a particularcustomer or may be developed for a general market

Software products may be

Generic - developed to be sold to a range ofdifferent customers

Bespoke (custom) - developed for a single customer accordingto their specification


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Importance of Software

The economies of ALL developed nations aredependent on software.

More and more systems are software controlled

Software engineering is concerned with theories,methods and tools for professional softwaredevelopment.

Expenditure on software represents asignificant fraction of Gross National Product (GNP) in

all developed countries.


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What is software engineering?

Software engineering is an engineering disciplinewhich is concerned with all aspects of softwareproduction

Software engineers should adopt a systematic and organisedapproach to their work

use appropriate tools and techniques depending on the problem to be solved,

the development constraints and

the resources available


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What is the difference between software

engineering and computer science?

Computer Science Software Engineering

is concerned with

Computer science theories are currently insufficient to act asa complete underpinning for software engineering, BUT it is

a foundation for practical aspects of software engineering

theory

fundamentals

the practicalities of developing

delivering useful software


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What is the difference between software

engineering and system engineering?

System engineering is concerned with all aspects of computer-based systems development including hardware, software andprocess engineering.

Software engineering is part of this process concerned with

developing the software infrastructure, control, applications anddatabases in the system. So this is a part of System engineering.

System engineers are involved in

system specification,

architectural design

Integration.


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What is a software process?

A set of activities whose goal is the development orevolution of software.

Generic activities in all software processes are:

Specification - what the system should do and itsdevelopment constraints

Development - production of the software system

Validation - checking that the software is what the customerwants

Evolution - changing the software in response to changingdemands.


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What are software engineering methods?

Structuredapproaches to software development which includesystemmodels, notations, rules, designadvice and processguidance.

Examples: DeMacro, JSD, UML etc.

Method Components:

Model descriptions: Descriptions of graphical models which should beproduced;

Rules: Constraints applied to systemmodels;

Recommendations: Advice on gooddesign practice; Process guidance: What activities to follow.


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What is CASE (Computer-Aided Software

Engineering)

Upper-CASE

Tools to support the early processactivities of requirements anddesign

Lower-CASE

Tools to support later activities such asprogramming, debugging and testing

Software systems which are intended to provideautomated support for software process activities,such as requirements analysis, system modelling,debugging and testing


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What are the attributes of good software?

The software shoulddeliver the required functionalityandperformance to the user and should be maintainable, dependableandacceptable.

Maintainability Software must evolve to meet changing needs (scalable);

Dependability Software must be trustworthy (reliable, securedand safe);

Efficiency Software shouldnot make wasteful use of system resources;

Acceptability Software must accepted by the users for which it was designed. Thismeans it must be understandable, usable and compatible with othersystems.


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What are the key challenges facing

Software Engineering?

Heterogeneity

Developing techniques for building software that can cope withheterogeneous platforms and execution environments;

Delivery

Developing techniques that lead to faster delivery of software;

Trust

Developing techniques that demonstrate that software can betrusted by its users.

Reliable, Securedand Safe.


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Generic Software Process Models

A simplified representation ofa software process,presented froma specific perspective

Examples ofprocess perspectives:

Workflow perspective represents inputs, outputs and

dependencies Data-flow perspective represents data transformationactivities

Role/action perspective represents the roles/activities of thepeople involved in software process

Generic process models

Waterfall

Evolutionary development

Formal transformation

Integration from reusable components


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Engineering Example

Building a house:

Land and finances

garden, garage, you are used to age wine,

enjoy to sit by the fireplace, lots of storage,

dont like Bauhaus

Architect will define number of floors and

rooms, orientation of the driveway, size of the

garage

type of bricks, color of the walls,

Construction

Entering

Living in the house

Fixing minor problems, leaking in the roof

System Feasibility

Software Plans and Requirements

Product Design

Detailed Design

Code

Integration (Product Verification)

Integration (System Test)

Operations and Maintenance


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he Waterfall Model

System Feasibility Validation

Plans +

RequirementsValidation

Product Design Verification

Detailed Design Verification

Code Unit Test

IntegrationProduct

Verification

Integration System Test

Operation +

MaintenanceRevalidationDidnt we forget something ?


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he Waterfall Model


Plans +




Code Unit Test

IntegrationProduct

Verification


Operation +

MaintenanceRevalidation


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Weaknesses:

Usually requirements change, are incomplete

or even not known

Communication ! (see Mars Orbiter)

Result: Thats not what I meant ! ( go back to

last step )

WF-Model reacts very statically:

Each stage must be completed before next

one starts

Review of Waterfall Model


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Plans +




Code Unit Test

IntegrationProduct

Verification


Operation +

MaintenanceRevalidation

Too expensiveDoesnt force to discipline

Dont show this to your boss !

otal FeedBack


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ValidationFinal

version

DevelopmentIntermediate

versions

SpecificationInitial

version

Outlinedescription

Concurrentactivities

Evolutionary Process Model


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Waterfall High risk for new systems because of specificationand

design problems.

Low risk for well-understooddevelopments using familiartechnology.

Prototyping

Low risk for new applications because specificationandprogram stay in step.

High risk because of lack of process visibility.

Transformational

High risk because ofneed for advanced technologyandstaff skills.

Process Model Problem


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Riskanalysis

Riskanalysis

Riskanalysis

Riskanalysis Proto-

type 1

Prototype 2

Prototype 3Opera-

tionalprotoype

Concept ofOperation

Simulations, models, benchmarks

S/Wrequirements

Requirementvalidation

DesignV&V

Product

design Detaileddesign

Code

Unit test

Integrationtest

AcceptancetestService Develop, verify

next-level product

Evaluate alternativesidentify, resolve risks

Determine objectivesalternatives and

constraints

Plan next phase

Integrationand test plan

Developmentplan

Requirements planLife-cycle plan

REVIEW

Spiral Process Model


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Focuses attention on reuse options.

Focuses attention on early error elimination.

Puts quality objectives up front.

Integrates development andmaintenance.

Provides a framework for hardware/softwaredevelopment.

Spiral Model Advantages


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Contractual development often specifiesprocess model anddeliverables inadvance.

Requires risk assessment expertise.

Spiral Model Problems


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User Programmer

SOFTWARE

Customer Designer

Programmers view:

Some (holy) lines of code

A technical challenge

A pet

...

he Human Factor


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User Programmer

SOFTWARE

Customer Designer

Users view: A miracle

A wonderful tool making things easier

An incombprehensible tool

unnecessarilly complicating life

Something that simply should work !

he Human Factor


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User Programmer

SOFTWARE

Customer DesignerCustomers view:

A hopefully affordable tool to enhance profit.

he Human Factor


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User Programmer

SOFTWARE

Customer DesignerDesigners view:

A reasonably complicated

tool to fulfill the needs

A technical challenge

he Human Factor


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Professional and ethical responsibility

Software engineering involves wider responsibilitiesthan simply the application of technical skills.

Software engineers must behave in an honest andethically responsible way if they are to be respected

as professionals. Ethical behaviour is more than simply upholding the

law.


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Question???

Documents

8[1]. Software Engineering Concepts