adv disadv
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CS 425/625 Software Engineering
Software Processes
Based on Chapter 4 of the textbook [SE-8] Ian Sommerville, Software Engineering, 8th Ed., Addison-
Wesley, 2006 and on Ch4 PPT presentation from http://www.software-engin.com/
September 10, 2007
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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 process = organized set of activities aimed at building a software system
• Software process model = an abstract representation of a software process
• Fundamental software process activities:– Software specification– Software design – Software implementation– Software validation– Software evolution
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Software Process Models: Waterfall..
• The Waterfall model [SE-8, 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 [SE-8, 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…
• CBSE process model [SE-8, 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:– Reduces considerably the software to be developed
“in-house”– Allows faster delivery– In principle, more reliable systems, due to using
previously tested 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 [SE-8, 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: ..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..
• Boehm’s Spiral Model [SE-8, 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.
• Main characteristics:– Also a hybrid model that support process iteration– The process is represented as a spiral, each loop in
the spiral representing a process phase– Four sectors per loop: objective setting, risk
assessment and reduction, development and validation, planning
– Risk is explicitly taken into consideration
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Software 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
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Process Activities: Specification
• Requirements engineering [SE-8, Fig. 4.6]
Feasibilitystudy
Requirementselicitation and
analysisRequirementsspecification
Requirementsvalidation
Feasibilityreport
Systemmodels
User and systemrequirements
Requirementsdocument
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Process Activities: Design & Implementation
• A general model for design [SE-8, Fig 4.7]
Architecturaldesign
Abstractspecification
Interfacedesign
Componentdesign
Datastructuredesign
Algorithmdesign
Systemarchitecture
Softwarespecification
Interfacespecification
Componentspecification
Datastructure
specification
Algorithmspecification
Requirementsspecification
Design activities
Design products
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Process Activities: Testing..
• The debugging process [SE-8, Fig 4.8]
Locateerror
Designerror repair
Repairerror
Re-testprogram
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Process Activities: .Testing.
• The testing process [SE-8, Fig 4.9]
Componenttesting
Systemtesting
Acceptancetesting
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Process Activities: ..Testing
• Testing phases in the SE process [SE-8, Fig. 4.10]
Requirementsspecification
Systemspecification
Systemdesign
Detaileddesign
Module andunit codeand test
Sub-systemintegrationtest plan
Systemintegrationtest plan
Acceptancetest plan
ServiceAcceptance
testSystem
integration testSub-system
integration test
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Process Activities: Evolution
• System evolution [SE-8, Fig 4.11]
Assess existingsystems
Define systemrequirements
Propose systemchanges
Modifysystems
Newsystem
Existingsystems
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The Rational Unified Process.
• RUP phases [SE-8, Fig 4.12]
Phase iteration
Inception Elaboration Construction Transition
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.The Rational Unified Process• RUP workflows [SE-8, Fig 4.13]
Workflow Description
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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CASE• Classification of CASE technology [SE-7, Fig 4.14]
Single-methodworkbenches
General-purposeworkbenches
Multi-methodworkbenches
Language-specificworkbenches
Programming TestingAnalysis and
design
Integratedenvironments
Process-centredenvironments
Filecomparators
CompilersEditors
EnvironmentsWorkbenchesTools
CASEtechnology