1 CS 425/625 Software CS 425/625 Software Engineering Engineering Software Processes Based on Chapter 4 of the textbook [SE-7] Ian Sommerville, Software Engineering, 7 th Ed., Addison- Wesley, 2004 and on Ch4 PPT presentation from http://www.software-engin.com / September 14, 2005
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1 CS 425/625 Software Engineering CS 425/625 Software Engineering Software Processes Based on Chapter 4 of the textbook [SE-7] Ian Sommerville, Software.
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Based on Chapter 4 of the textbook [SE-7] Ian Sommerville, Software Engineering, 7th Ed., Addison-Wesley, 2004
and on Ch4 PPT presentation from http://www.software-engin.com/
September 14, 2005
2
Outline
Software Process Models Waterfall model Evolutionary development Component-based software engineering Incremental model Spiral model
Software Process Activities Specification Design and implementation Validation Evolution
The Rational Unified Process Computer-Aided Software Engineering
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Software Process Models
Software processSoftware process = organized set of activities aimed at = organized set of activities aimed at building a software systembuilding a software system
Software process modelSoftware process model = an abstract representation = an abstract representation of a software processof a software process
Fundamental software process activities:Fundamental software process activities: Software specificationSoftware specification Software design Software design Software implementationSoftware implementation Software validationSoftware validation Software evolutionSoftware evolution
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Software Process Models: Waterfall..
The Waterfall modelThe Waterfall model [SE-7, Fig 4.1][SE-7, Fig 4.1]
Requirementsdefinition
System andsoftware design
Implementationand unit testing
Integration andsystem testing
Operation andmaintenance
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Software Process Models: .Waterfall.
Main characteristics: Also called classic software life cycle or
sequential model Process activities (phases/stages) are clearly
separated After a number of iterations, phases of the life
cycle (such as specification and design) are “frozen”
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Software Process Models: ..Waterfall
Advantages: Organized approach, provides robust separation of phases Reflects common engineering practice
Disadvantages: Doesn’t cope well with changes required by the client Development teams might wait for each other A working version of the product is available only late
Applicability: When requirements are well known and few changes are
likely to be needed Can be used also for parts of larger software systems
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Software Process Models: Evolutionary Development…
Evolutionary Development model Evolutionary Development model [SE-7, Fig 4.2][SE-7, Fig 4.2]
ValidationFinal
version
DevelopmentIntermediate
versions
SpecificationInitial
version
Outlinedescription
Concurrentactivities
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Software Process Models: .Evolutionary Development..
Main characteristics: The phases of the software construction are interleaved Feedback from the user is used throughout the entire process
The software product is refined through many versions
Types of evolutionary development: Exploratory development Throw-away prototyping
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Software Process Models: ..Evolutionary Development.
Advantages: Deals constantly with changes Provides quickly an initial version of the system Involves all development teams
Disadvantages: Quick fixes may be involved “Invisible” process, not well-supported by documentation The system’s structure can be corrupted by continuous
change
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Software Process Models: …Evolutionary Development
Disadvantages [cont’d]: Special tools and techniques may be necessary The client may have the impression the first version is very
close to the final product and thus be less patient
Applicability: When requirements are not well understood When the client and the developer agree on a “rapid
prototype” that will be thrown away Good for small and medium-sized software systems
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Software Process Models: Component-based Software Engineering…
CBSECBSE process model process model [SE-7, Fig 4.3][SE-7, Fig 4.3]
Requirementsspecification
Componentanalysis
Developmentand integration
System designwith reuse
Requirementsmodification
Systemvalidation
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Software Process Models: .Component-based Software Engineering..
Main characteristics: Makes intensive use of existing reusable components The focus is on integrating the components rather than on
creating them from the scratch
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Software Process Models: ..Component-based Software Engineering.
Advantages:Advantages: Reduces considerably the software to be developed “in-house”Reduces considerably the software to be developed “in-house” Allows faster deliveryAllows faster delivery In principle, more reliable systems, due to using previously In principle, more reliable systems, due to using previously
tested componentstested components
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Software Process Models: …Component-based Software Engineering
Disadvantages: Compromises in requirements are needed Less control over the system’s evolution
Applicability: When there is a pool of existing components that could
satisfy the requirements of the new product Emerging trend: integration of web services from a range
of suppliers
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Software Process Models: Incremental Development…
The Incremental model The Incremental model [SE-7, Fig 4.4][SE-7, Fig 4.4]
Valida teincrement
Develop systemincrement
Design systemarchitecture
Integrateincrement
Valida tesystem
Define outline requirements
Assign requirements to increments
System incomplete
Finalsystem
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Software Process Models: .Incremental..
Main characteristics: Hybrid model that combines elements of the waterfall and
evolutionary paradigms The specification, design, and implementation phases are
broken in smaller increments
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Software Process Models: ..Software Process Models: ..Incremental..
Advantages: Provides better support for process iteration Reduces rework in the software construction process Some decisions on requirements may be delayed Allows early delivery of parts of the system Supports easier integration of sub-systems Lower risk of project failure Delivery priorities can be more easily set
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Software Process Models: ...Incremental
Disadvantages: Increments need be relatively small Mapping requirements to increments may not be easy Common software facilities may be difficult to identify
Applicability: When it is possible to deliver the system “part-by-part”
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Software Process Models: Spiral Model..Software Process Models: Spiral Model..
Boehm’s Spiral Model [SE, Fig 4.5]
Riskanalysis
Riskanalysis
Riskanalysis
Riskanalysis Proto-
type 1
Prototype 2Prototype 3
Opera-tionalprotoype
Concept ofOperation
Simulations, models, benchmarks
S/Wrequirements
Requirementvalidation
DesignV&V
Productdesign Detailed
design
CodeUnit test
IntegrationtestAcceptance
testService Develop, verifynext-level product
Evaluate alternativesidentify, resolve risks
Determine objectivesalternatives and
constraints
Plan next phase
Integrationand test plan
Developmentplan
Requirements planLife-cycle plan
REVIEW
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Software Process Models: .Spiral Model.Software Process Models: .Spiral Model.
Main characteristics:Main characteristics: Also a hybrid model that support process iterationAlso a hybrid model that support process iteration The process is represented as a spiral, each loop in the spiral The process is represented as a spiral, each loop in the spiral
representing a process phaserepresenting a process phase Four sectors per loop: objective setting, risk assessment and Four sectors per loop: objective setting, risk assessment and
reduction, development and validation, planningreduction, development and validation, planning Risk is explicitly taken into considerationRisk is explicitly taken into consideration
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Software Process Models: ..Spiral ModelSoftware Process Models: ..Spiral Model
Advantages: Risk reduction mechanisms are in place Supports iteration and reflects real-world practices Systematic approach
Disadvantages: Requires expertise in risk evaluation and reduction Complex, relatively difficult to follow strictly Applicable only to large systems
Applicability: Internal development of large systems
Business modelling The business processes are modelled using business use cases.
Requirements Actors who interact with the system are identified and use cases aredeveloped to model the system requirements.
Analysis and design A design model is created and documented using architecturalmodels, component models, object models and sequence models.
Implementation The components in the system are implemented and structured intoimplementation sub-systems. Automatic code generation from designmodels helps accelerate this process.
Test Testing is an iterative process that is carried out in conjunction withimplementation. System testing follows the completion of theimplementation.
Deployment A product release is created, distributed to users and installed in theirworkplace.
Configuration andchange management
This supporting workflow managed changes to the system (seeChapter 29).
Project management This supporting workflow manages the system development (seeChapter 5).
Environment This workflow is concerned with making appropriate software toolsavailable to the software development team.
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CASECASE Classification of CASE technology Classification of CASE technology [SE-7, Fig 4.14][SE-7, Fig 4.14]