cc20o7n software engineering 1 cc2007n software engineering 1 part 1 introduction to software...

CC20O7N Software Engineering 1

CC2007NCC2007NSoftware Engineering 1Software Engineering 1

Part 1Part 1Introduction to Software Introduction to Software

EngineeringEngineering


ContentsContents

• Software Application Areas• Problems of Large Software Systems• The Software Crisis• What Is Software Engineering?• Software Life Cycle - Generic Phases/Stages


Software Application AreasSoftware Application Areas• System software• Application/Business software• Engineering and scientific software• Embedded software• Product-line software (PC software)• Web-applications• Artificial intelligence software


Problems with Large Problems with Large Software SystemsSoftware Systems

• Delivery• Costs• Correctness• Efficiency


Software Costs Software Costs (world-wide)(world-wide)

0

100

200

300

400

1985 1990 1995

$ bi

llion

s


Relative Cost of Hardware Relative Cost of Hardware and Softwareand Software

0

50

100

1955 1960 1965 1970 1975 1980 1985 1990

% C

ost a

nd E

ffort Hardware

Software

0

50

100

1955 1960 1965 1970 1975 1980 1985 1990

% C

ost a

nd E

ffort

0

50

100

1955 1960 1965 1970 1975 1980 1985 1990

% C

ost a

nd E

ffort Hardware

Software


Software EngineeringSoftware Engineering

• Concerned with:– building large programs – maintenance– efficiency of development and maintenance– quality– management


Three Major Phases in the Three Major Phases in the Software Life CycleSoftware Life Cycle

• Definition phase• Development phase• Maintenance phase


Generic Stages in the Generic Stages in the Software Life CycleSoftware Life Cycle

}

• Strategy planning• Feasibility study• Requirements analysis

Definition phase}Development

phase

Design (system design, detailed design)

Implementation Testing

}Maintenance Maintenance phase


Costs of Software Life Cycle StagesCosts of Software Life Cycle Stages

%

0

50

100

Analysis andDesign

Coding Testing Maintenance


SummarySummary• Discussed

– the importance of software and the wide range of software applications

– problems with software - the software crisis• Presented

– several definitions and the main goals of software engineering

• Identified– generic phases and stages in the software life cycle


CC2007NCC2007NSoftware Engineering 1Software Engineering 1

Part 2Part 2

The Software Life Cycle ModelsThe Software Life Cycle Models


ContentsContents

• Waterfall Model• Evolutionary Models• Incremental Development


Waterfall Model - BasicWaterfall Model - Basic

Feasi-bilityStudy Req.

AnalysisDesign

TestingMainte-nance

Implemen-tation


AnalysisDesign

TestingMainte-nance

Implemen-tation


Waterfall ModelWaterfall ModelAdvantages & DisadvantagesAdvantages & Disadvantages

• It is easy to identify milestones (+)• It is easy to separate one stage from another

(+)• Documentation is produced(+)• It is totally unrealistic! (---)


Waterfall Model - EnhancedWaterfall Model - Enhanced


AnalysisDesign

TestingMainte-nance

Implemen-tation


AnalysisDesign

TestingMainte-nance

Implemen-tation


Waterfall – EnhancedWaterfall – EnhancedAdvantages & DisadvantagesAdvantages & Disadvantages

• It is easy to identify milestones (+)• It is easy to separate one stage from another (+)• Software is properly documented (+)• Premature requirements, design, etc. (-)• It assumes that requirements can be precisely specified

(-)• It requires the customer to be patient (-)• It is still unrealistic!


Prototyping ProcessPrototyping Process

Establish prototype objectives

Define prototype

functionality

Develop prototype

Evaluate prototype

Prototyping plan

Outline definition

Executable prototype

Evaluationreport


Prototype (as a tool for Prototype (as a tool for requirements analysis) - Benefitsrequirements analysis) - Benefits

• Misunderstandings between software developers and users identified as the system functions are demonstrated

• Missing user services may be detected• Difficult-to-use or confusing user services may be

identified and refined• Incomplete/inconsistent requirements found as the

prototype is developed• A working, albeit limited, system is available quickly for

demonstration to management


Throw-Away PrototypingThrow-Away Prototyping

* At this point the prototype is thrown away!** Development phase of the actual system

Establish outline spec.

Design & implement

system

Develop prototype

Evaluate prototype

Specify system

**

*

Validate system


Throw-Away Prototype - ProblemsThrow-Away Prototype - Problems

• Sometimes the cost of prototype development represents an unacceptably large fraction of the total cost

• Customers are likely to force the developer to convert the prototype to the working system using a few fixes

• The developer may become familiar with the prototype and reluctant to discard it


Evolutionary PrototypingEvolutionary Prototyping

Develop abstract

specification

system

Deliver system

System adequate?

NO

YES

Develop abstract

specification

Develop abstract

specificationBuild prototype Use prototype

system

Deliver system

System adequate?

NO

YES


Evolutionary PrototypingEvolutionary PrototypingAdvantages & DisadvantagesAdvantages & Disadvantages

• Systems are developed and delivered rapidly (+)• Costs are reduced (+)• User involvement! (+)• The development process is ‘invisible’ to managers (+)• Systems are usually poorly structured! (-)


Incremental DevelopmentIncremental Development

Integrate incrementIntegrate increment

System complete?

Designsystem

architecture

Specifysystem

increment

Buildsystem

incrementValidate

increment

Definesystem

deliverables

Validatesystem

Deliver finalsystem

YES

NO

Reproduced from: Sommerville

System complete?

Designsystem

architecture

Specifysystem

increment

Specifysystem

increment

Buildsystem

increment

Buildsystem

incrementValidate

increment

Definesystem

deliverables

Validatesystem

Deliver finalsystem

YES

NO

Reproduced from: Sommerville


Incremental DevelopmentIncremental DevelopmentAdvantages & DisadvantagesAdvantages & Disadvantages

• No ‘big bang’ effect (+)• Attention on the essential features (+)• Customers can use the ‘partial’ software as soon as it is available (+)• Early increments can provide a useful feedback (+)• The requirements tend to constrained by the architecture (-)• Problems with contracts (-)• Difficult to map the customer’s requirements onto increments (-)• Problems with basic facilities (-)


SummarySummary• Software life cycle models

– all of them include the main generic stages– logic of the software process is different in each

• The spiral model, which subsumes the other models, should be investigated by students.

• Object orientation – emphasis on reusability– software development process will become one of

assembly rather than one of creation

cc20o7n software engineering 1 cc2007n software engineering 1 part 1 introduction to software...

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