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© The McGraw-Hill Companies, 2007

Object-Oriented andClassical Software

Engineering

Seventh Edition, WCB/McGraw-Hill, 2007

Stephen R. Schachsrs@vuse.vanderbilt.edu

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CHAPTER 1

THE SCOPE OF SOFTWARE

ENGINEERING

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Outline

Historical aspects Economic aspects Maintenance aspects Requirements, analysis, and design aspects Team development aspects Why there is no planning phase

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Outline (contd)

Why there is no testing phase Why there is no documentation phase The object-oriented paradigm The object-oriented paradigm in perspective Terminology Ethical issues

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1.1 Historical Aspects

1968 NATO Conference, Garmisch, Germany

Aim: To solve the software crisis

Software is deliveredLateOver budgetWith residual faults

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Standish Group Data

Data on9236projectscompletedin 2004

Figure 1.1

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Cutter Consortium Data

2002 survey of information technologyorganizations78% have been involved in disputes ending in litigation

For the organizations that entered into litigation:In 67% of the disputes, the functionality of the

information system as delivered did not meet up to theclaims of the developers

In 56% of the disputes, the promised delivery dateslipped several times

In 45% of the disputes, the defects were so severe thatthe information system was unusable

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Conclusion

The software crisis has not been solved

Perhaps it should be called the softwaredepressionLong durationPoor prognosis

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1.2 Economic Aspects

Coding method CMnew is 10% faster than currentlyused method CMold. Should it be used?

Common sense answerOf course!

Software Engineering answerConsider the cost of trainingConsider the impact of introducing a new technologyConsider the effect of CMnew on maintenance

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1.3 Maintenance Aspects

Life-cycle modelThe steps (phases) to follow when building softwareA theoretical description of what should be done

Life cycleThe actual steps performed on a specific product

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Waterfall Life-Cycle Model

Classical model (1970)

Figure 1.2

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Typical Classical Phases

Requirements phaseExplore the conceptElicit the client’s requirements

Analysis (specification) phaseAnalyze the client’s requirementsDraw up the specification documentDraw up the software project management plan“What the product is supposed to do”

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Typical Classical Phases (contd)

Design phaseArchitectural design, followed byDetailed design“How the product does it”

Implementation phaseCodingUnit testingIntegrationAcceptance testing

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Typical Classical Phases (contd)

Postdelivery maintenanceCorrective maintenancePerfective maintenanceAdaptive maintenance

Retirement

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1.3.1 Classical and Modern Views of Maintenance

Classical maintenanceDevelopment-then-maintenance model

This is a temporal definitionClassification as development or maintenance depends

on when an activity is performed

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Classical Maintenance Defn — Consequence 1

A fault is detected and corrected one day after thesoftware product was installedClassical maintenance

The identical fault is detected and corrected oneday before installationClassical development

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Classical Maintenance Defn — Consequence 2

A software product has been installed

The client wants its functionality to be increasedClassical (perfective) maintenance

The client wants the identical change to be madejust before installation (“moving target problem”)Classical development

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Classical Maintenance Definition

The reason for these and similar unexpectedconsequencesClassically, maintenance is defined in terms of the time

at which the activity is performed

Another problem:Development (building software from scratch) is rare

todayReuse is widespread

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Modern Maintenance Definition

In 1995, the International Standards Organizationand International Electrotechnical Commissiondefined maintenance operationally

Maintenance is nowadays defined asThe process that occurs when a software artifact is

modified because of a problem or because of a need forimprovement or adaptation

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Modern Maintenance Definition (contd)

In terms of the ISO/IEC definitionMaintenance occurs whenever software is modifiedRegardless of whether this takes place before or after

installation of the software product

The ISO/IEC definition has also been adopted byIEEE and EIA

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Maintenance Terminology in This Book

Postdelivery maintenanceChanges after delivery and installation [IEEE 1990]

Modern maintenance (or just maintenance)Corrective, perfective, or adaptive maintenance

performed at any time [ISO/IEC 1995, IEEE/EIA 1998]

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1.3.2 The Importance of Postdelivery Maintenance

Bad software is discarded

Good software is maintained, for 10, 20 years ormore

Software is a model of reality, which is constantlychanging

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Time (= Cost) of Postdelivery Maintenance

(a) Between 1976 and 1981(b) Between 1992 and 1998

Figure 1.3

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The Costs of the Classical Phases

Surprisingly, the costs of the classical phaseshave hardly changed

Figure 1.4

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Consequence of Relative Costs of Phases

Return to CTold and CTnew

Reducing the coding cost by 10% yields at most a0.85% reduction in total costsConsider the expenses and disruption incurred

Reducing postdelivery maintenance cost by 10%yields a 7.5% reduction in overall costs

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1.4 Requirements, Analysis, and Design Aspects

The earlier we detect and correct a fault, the less itcosts us

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Requirements, Analysis, and Design Aspects (contd)

Figure 1.5

The cost ofdetecting andcorrecting afault at eachphase

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Requirements, Analysis, and Design Aspects (contd)

Thepreviousfigureredrawnon alinearscale

Figure 1.6

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Requirements, Analysis, and Design Aspects (contd)

To correct a fault early in the life cycleUsually just a document needs to be changed

To correct a fault late in the life cycleChange the code and the documentationTest the change itselfPerform regression testingReinstall the product on the client’s computer(s)

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Requirements, Analysis, and Design Aspects (contd)

Between 60 and 70% of all faults in large-scaleproducts are requirements, analysis, and designfaults

Example: Jet Propulsion Laboratory inspections1.9 faults per page of specifications0.9 per page of design0.3 per page of code

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Conclusion

It is vital to improve our requirements, analysis,and design techniquesTo find faults as early as possibleTo reduce the overall number of faults (and, hence, the

overall cost)

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1.5 Team Programming Aspects

Hardware is cheapWe can build products that are too large to be written by

one person in the available time

Software is built by teamsInterfacing problems between modulesCommunication problems among team members

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1.6 Why There Is No Planning Phase

We cannot plan at the beginning of the project—we do not yet know exactly what is to be built

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Planning Activities of the Classical Paradigm

Preliminary planning of the requirements andanalysis phases at the start of the project

The software project management plan is drawnup when the specifications have been signed offby the client

Management needs to monitor the SPMPthroughout the rest of the project

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Conclusion

Planning activities are carried out throughout thelife cycle

There is no separate planning phase

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1.7 Why There Is No Testing Phase

It is far too late to test after development andbefore delivery

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Testing Activities of the Classical Paradigm

VerificationTesting at the end of each phase (too late)

ValidationTesting at the end of the project (far too late)

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Conclusion

Continual testing activities must be carried outthroughout the life cycle

This testing is the responsibility ofEvery software professional, andThe software quality assurance group

There is no separate testing phase

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1.8 Why There Is No Documentation Phase

It is far too late to document after developmentand before delivery

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Documentation Must Always be Current

Key individuals may leave before thedocumentation is complete

We cannot perform a phase without having thedocumentation of the previous phase

We cannot test without documentation

We cannot maintain without documentation

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Conclusion

Documentation activities must be performed inparallel with all other development andmaintenance activities

There is no separate documentation phase

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1.9 The Object-Oriented Paradigm

The structured paradigm was successful initiallyIt started to fail with larger products (> 50,000 LOC)

Postdelivery maintenance problems (today, 70 to80% of total effort)

Reason: Structured methods areAction oriented (e.g., finite state machines, data flow

diagrams); orData oriented (e.g., entity-relationship diagrams,

Jackson’s method);But not both

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The Object-Oriented Paradigm (contd)

Both data and actions are of equal importance

Object:A software component that incorporates both data and

the actions that are performed on that data

Example:Bank account

Data: account balance Actions: deposit, withdraw, determine balance

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Structured versus Object-Oriented Paradigm

Information hiding Responsibility-driven design Impact on maintenance,

development

Figure 1.7

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Information Hiding

In the object-oriented versionThe solid line around accountBalance denotes that

outside the object there is no knowledge of howaccountBalance is implemented

In the classical versionAll the modules have details of the implementation of

account_balance

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Strengths of the Object-Oriented Paradigm

With information hiding, postdelivery maintenanceis saferThe chances of a regression fault are reduced

Development is easierObjects generally have physical counterpartsThis simplifies modeling (a key aspect of the object-

oriented paradigm)

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Strengths of the Object-Oriented Paradigm (contd)

Well-designed objects are independent unitsEverything that relates to the real-world item being

modeled is in the corresponding object —encapsulation

Communication is by sending messagesThis independence is enhanced by responsibility-driven

design (see later)

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Strengths of the Object-Oriented Paradigm (contd)

A classical product conceptually consists of asingle unit (although it is implemented as a set ofmodules)The object-oriented paradigm reduces complexity

because the product generally consists of independentunits

The object-oriented paradigm promotes reuseObjects are independent entities

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Responsibility-Driven Design

Also called design by contract

Send flowers to your mother in ChicagoCall 1-800-flowersWhere is 1-800-flowers?Which Chicago florist does the delivery?Information hidingSend a message to a method [action] of an object

without knowing the internal structure of the object

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Classical Phases vs Object-Oriented Workflows

There is no correspondence between phases andworkflows

Figure 1.8

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Analysis/Design “Hump”

Structured paradigm:There is a jolt between analysis (what) and design

(how)

Object-oriented paradigm:Objects enter from the very beginning

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Analysis/Design “Hump” (contd)

In the classical paradigmClassical analysis

Determine what has to be done

Design Determine how to do it Architectural design — determine the modules Detailed design — design each module

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Removing the “Hump”

In the object-oriented paradigmObject-oriented analysis

Determine what has to be done Determine the objects

Object-oriented design Determine how to do it Design the objects

The difference between the two paradigms isshown on the next slide

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In More Detail

Objects enter hereFigure 1.9

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Object-Oriented Paradigm

Modules (objects) are introduced as early as theobject-oriented analysis workflowThis ensures a smooth transition from the analysis

workflow to the design workflow

The objects are then coded during theimplementation workflowAgain, the transition is smooth

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1.10 The Object-Oriented Paradigm in Perspective

The object-oriented paradigm has to be usedcorrectlyAll paradigms are easy to misuse

When used correctly, the object-oriented paradigmcan solve some (but not all) of the problems of theclassical paradigm

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The Object-Oriented Paradigm in Perspective (contd)

The object-oriented paradigm has problems of itsown

The object-oriented paradigm is the bestalternative available todayHowever, it is certain to be superceded by something

better in the future

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1.11 Terminology

Client, developer, user

Internal software

Contract software

Commercial off-the-shelf (COTS) software

Open-source softwareLinus’s Law

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Terminology (contd)

Software

Program, system, product

Methodology, paradigmObject-oriented paradigmClassical (traditional) paradigm

Technique

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Terminology (contd)

Mistake, fault, failure, error

Defect

Bug “A bug crept into the code” instead of“I made a mistake”

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Object-Oriented Terminology

Data component of an objectState variableInstance variable (Java)Field (C++)Attribute (generic)

Action component of an objectMember function (C++)Method (generic)

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Object-Oriented Terminology (contd)

C++: A member is either anAttribute (“field”), or aMethod (“member function”)

Java: A field is either anAttribute (“instance variable”), or aMethod

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1.12 Ethical Issues

Developers and maintainers need to beHard workingIntelligentSensibleUp to date and, above all,Ethical

IEEE-CS ACM Software Engineering Code ofEthics and Professional Practicewww.acm.org/serving/se/code.htm