introduction to software engineering - gowthamivuppala · somnuk keretho/kasetsart university...

Somnuk Keretho/Kasetsart University

Introduction to Software Engineering

Somnuk Keretho, Assistant Professor

Department of Computer Engineering

Faculty of Engineering, Kasetsart University

Email: [email protected]

URL: http://www.cpe.ku.ac.th/~sk

Somnuk Keretho/Kasetsart University 2

Outline of this presentation

• Scope of Software Engineering

• Object-Oriented Software Development

• Software Process

• Software Life-Cycle Models

• Object Orientation

• Software Quality Assessment

Reference to Chapter 1/2/3 of “Software Engineering with JAVA”, S.R. Schach, McGraw-Hill, 1997.


Scope of Software Engineering

• Software engineering is a discipline whose aimis the production of fault-free software, that isdelivered on time, within budget, and satisfiesthe user’s needs.



• Historical Aspects:– 1967, a NATO group coined the term “Software

Engineering”

– 1968 NATO Software Engineering Conferenceconcurred that “Software production should be anengineering-like activity”.

– Using philosophies and paradigms of establishedengineering disciplines to solve “Software Crisis: thatthe quality of software was generally unacceptably lowand that deadlines and cost limits were not being met”.



• Economic Aspects– Software Engineering v.s. Computer Science

• The computer scientist investigates several ways to producesoftware, some good and some bad.

• But the software engineer is interested in only those techniquesthat make sound economic sense.

For example: A coding technique that can execute veryefficiently but with higher maintenance cost may not be a goodchoice.



• Maintenance Aspects– Software Life Cycle / Software Process

• Requirements Phase

• Specification (Analysis) Phase

• Planning Phase

• Design Phase

• Implementation Phase

• Integration Phase

• Maintenance Phase (highest cost among all these phases)– Corrective, Perfective, and Adaptive Maintenance

• Retirement



Requirement 2%Specification 4%Planning 1%Design 6%Module Coding 5%Module Testing 7%Integration 8%Maintenance 76%

Maintenance67%

Approximate relative costs of the phases of the software life cycle.

Maintenance is so important, a major aspect of software engineeringconsists of techniques, tools, and practices that lead to a reduction inmaintenance cost.



• Specification and Design Aspects– Software professionals are humans, and humans can

make error.

– The fact that so many faults are introduced early in thesoftware life cycle, highlights another important aspectsof software engineering, namely, techniques that yieldbetter specifications and designs.

• For example, reducing specification and design faults by 10%will reduce the overall number of faults by 6-7%.



• Team Programming Aspects– Most software being developed and maintained by a

team of software engineers

– Scope of software engineering must also includetechniques for ensuring that teams are properlyorganized and managed.

• For example, team programming leads to interface problemsamong code components and communication problems amongteam members.



• Several techniques have been suggested to help solve thesoftware crisis.– ~1975-1985: Structured Paradigm

• Structured Systems Analysis, Composite/Structured Design, StructuredProgramming, Structured Testing

• Lead to major improvements for software industry.

• But only good for small programs (say, 5,000-50,000 lines of codes)

• Not scale well with today larger programs (say, 500.000-5,000,000 LOC)

• Not so good in software maintenance aspects, (for instance, because of theseparation of action-oriented and data-oriented in structured paradigm).

– Object-Oriented Paradigm• An object is a unified software component that incorporates both data and

actions that operate of those data.



Structured Paradigm• Requirement Phase

• Specification (Analysis) Phase

• Planning Phase

• Design Phase

• Implementation Phase


• Maintenance Phase

• Retirement

Object-Oriented Paradigm• Requirement Phase

• Object-Oriented AnalysisPhase

• Planning Phase

• Object-Oriented Design Phase

• Object-OrientedProgramming Phase


• Maintenance Phase

• Retirement

Comparison of life cycles of structures paradigm and object-oriented paradigm.


Object-Oriented Software Development

• Three key words.– Software

– Development

– Object Orientation

• Let us look at each in turn


Software

• Programs

• Documentation during the development ofprograms (e.g. specification)

• Primary aids for running the programs (e.g.user manuals)

• Secondary aids for running the programs (e.g.key boards overlays)

Software is not just programs!


Software Life Cycle

• Software is like humans.

• It has a life cycle.

• Software in a system is conceptualized first.

• It becomes obsolescent at the end.

• The period in between is called the software lifecycle.


Software Life Cycle Models

• Build-and-Fix Model

• Waterfall Model

• Rapid prototyping model

• Incremental Model

• Spiral Model

• Concurrent Development Model

• Formal Methods Model

For the first four items, please refer to Chapter 3 of “Software Engineering with JAVA”, S.R. Schach, McGraw-Hill, 1997.


Built-and-Fix Model

• Unfortunately, many s/w products aredeveloped with built-and-fix model.

• Without specification or any attempt in design,just build a product, and reworked as manytimes needed to satisfy the customer.

• Unsatisfactory for any size of s/w development,we better specify the various phases of softwareprocess.


Why use a life cycle model?

• Life cycle model breaks down the developmentprocess into phases or stages.

• This is because software development iscomplex.

• Breaking down the development process makesit easier to manage.

• Each phase can be performed in various ways.


Waterfall ModelRequirement Verify

Implementation Testing

Planning Verify

Retirement

Design Verify

Integration Testing

Operation Mode

Specification Verify

Development

Maintenance

Changed Requirements verify


Rapid Prototyping Model

• A rapid prototype is a working model that isfunctionally equivalent to a subset of the product(internal structure is not concerned yet).

• The sole use of rapid prototyping is to determine whatthe client’s real needs are, construct the rapidprototype as rapidly as possible to speed up the s/wdevelopment process.


Rapid Prototyping ModelRapid Prototype Verify

Implementation Testing

Planning Verify

Retirement

Design Verify

Integration Testing

Operation Mode


Development

Maintenance

Changed Requirements verify


Incremental Model

• The s/w product is designed, implemented,integrated, and tested as a series of incrementalbuilds, where a build consists of code piecesfrom various modules interacting to provide aspecific functional capability.

• It is sometimes necessary to re-specify,re-design, re-code, or at worst, throw awaywhat has already been completed and startagain.


Incremental ModelRequirement Verify

Planning Verify

Retirement

Architectural Design Verify

Operation Mode


Development

Maintenance

For each build: Perform detailed design, implementation, and integration. Test.

Deliver to client.


Spiral Model

• The idea of minimizing risk via the use ofprototypes and other means is the conceptunderlying the spiral model.

• A simplified spiral model is as a waterfallmodel with each phase preceded by riskanalysis.– Before commencing each phase, an attempt is made to

control (resolve) the risks. If it is impossible to resolveall the significant risks at a stage, then the project isimmediately terminated.


Full Spiral Model [Boehm, IEEE 1998]

ReviewCommitment

Partition

Determineobjectives, alternatives,constraints

Progressthrough steps

Cumulativecost

Plan next phase

Develop, verifynext-level product

Evaluate alternatives,identify, resolve risks

RiskAnalysis

Concept ofOperation

Requirement planlife-cycle plan

Prototype 1 Prototype 2 Prototype 3OperationalPrototype

RiskAnalysis

RiskAnalysis

RiskAnalysis

Simulations, models, benchmarks

SoftwareRequirements

SoftwareProductDesign

DetailedDesign

Development Plan

Integration and TestPlan

ImplementationAcceptanceTest

IntegrationTest

UnitTest

CodeRequirementValidation

Design validationand verification


Software Development

• Software is developed using a life cycle model.

• Just a life cycle model is insufficient fordevelopment.

• We need:– A broad philosophy

– A set of tools which support the philosophy.

– A language which supports the philosophy.


Software Development Paradigm

• A paradigm provides a general approach towork during each phase of the life cycle model.

• A paradigm is a broad philosophy.

• A paradigm is not a specific model.


Some Software Development Paradigms

• Functional Composition

• Logic Programming

• Structured Development

• Object Orientation


Functional Development

• A problem is expressed in termed of a set ofmathematical functions.– e.g. Double(x) = Add(x, x).

• An algorithm is not specified.

• Language such as Miranda, Gofer, Haskellsupport this paradigm.

• Poor execution speed.


Logic Programming

• Consists of a problem description only.– e.g. Factorial(0) = 1.

Factorial(N) = N x Factorial(N -1).

• Doesn’t describe how to solve the problem.

• Languages Prolog & Lisp support thisparadigm.


Structured Development

• Also called SASD, SADT & FunctionalDecomposition.

• Breaks the system into processes & decomposesthem.

• Languages C, Fortran, Pascal, Cobol, Basicand a lot more support this paradigm.

• By far the most popular paradigm.


Object Orientation

• Most recent paradigm.

• Treats a problem as a collection of objects.

• Becoming very popular now.

• More and more languages support thisparadigm now.


Tools for OO

• Rambaugh (OMT)

• Coad-Yourdon

• Booch

• UML


Languages for OO

• C++

• Smalltalk

• Eiffel

• Object C

• Object Pascal

• Java


Software Quality Assessment

• CMM by SEI

• ISO 9000

introduction to software engineering - gowthamivuppala · somnuk keretho/kasetsart university...

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