CS 425/625 Software Engineering Software Processes

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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 21, 2009

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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

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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
• Doesnt 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

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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 systems structure can be corrupted by
  continuous change

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Software Process Models Evolutionary
Development

• Disadvantages contd
• 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

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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 systems 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

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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 features 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..

• Boehms Spiral Model SE-8, Fig 4.5

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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

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Process Activities Design Implementation

• A general model for design SE-8, Fig 4.7

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Process Activities Testing..

• The debugging process SE-8, Fig 4.8

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Process Activities .Testing.

• The testing process SE-8, Fig 4.9

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Process Activities ..Testing

• Testing phases in the SE process SE-8, Fig.
  4.10

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Process Activities Evolution

• System evolution SE-8, Fig 4.11

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The Rational Unified Process.

• RUP phases SE-8, Fig 4.12

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.The Rational Unified Process

• RUP workflows SE-8, Fig 4.13

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CASE

• Classification of CASE technology SE-7, Fig
  4.14