CS 361 Software Engineering Chapter 2: Modeling the Process and Life Cycle

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CS 361 Software EngineeringChapter 2
Modeling the Process and Life Cycle

• June 30, 2008

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Elements of Software Engineering

• Methods
• Technical how tos to support software
• development tasks
• Languages
• Notations to support methods
• Tools
• (Semi-) automated support for (the usage
  of)
• methods and languages
• Processes

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What is a Process?

• Coordination and management of software
  development tasks supported by methods,
  languages, and tools
• A series of steps involving activities,
  constraints, resources

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Development Process and Product Lifecycle
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Process

• Process Characteristics
• -The process describes the major activities
• - Each process activity has input, output
  and
• exit criteria

• The activities are organized in sequences

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Process and Roles
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System Development process - Basic activities

• Requirements analysis and definition
• System design (overall design)
• Program design (detailed design)
• Program implementation (writing the programs)
• System Integration
• Testing
• System delivery
• (Maintenance)
• (Disposal)

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Software Development Models

• Waterfall model
• Iterative models
• Spiral model
• RUP model
• Agile model
• Extreme Programming (XP)
• Others

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Waterfall model (70)
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Waterfall model - characteristics
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Waterfall model documents (SE - Ian Sommerville)
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Waterfall Model -features

• Legacy model
• has been in use since the 1970s
• Characterized by completely finishing a step
  before proceeding to the next step.
• - once a step is finished, it is not revisited
• (when this model is rigidly followed).
• Large government agencies still use forms of this
  model
• - prefer to spend large amounts of effort on
• analysis and requirements before awarding
• contracts.

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Waterfall Model - Pros

• Very well distinguished process (easy to
  understand)
• Every steps in the model completes with a
  MILESTONE
• A milestone is defined as a completion of set of
  documents
• Well defined inputs and outputs of the activities
• Precisely define different roles of developers

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Waterfall Model - Cons

• Software engineers cannot predict the future and
  anticipate every requirement and problem
• This model is not flexible enough to allow
  requirements to evolve.
• Software is usually developed with a great deal
  of iteration

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The software process in reality
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Where the waterfall model works fine?

• Established procedures and technologies
• Not too much requirements changes
• Well organized projects with precisely defined
  roles
• Repeatable projects
• Big projects not time and budget critical
• What are characteristics of today's development?
• How does Waterfall model fit for them?

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Requirements on the development process today

• Requirements
• -Time-to market
• - User Interfaces
• - Possibility for integration with other
  products
• - Using standard and de-facto standard
  solutions
• - Using already existing components

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Requirements on the development process today

• Permanent change of technologies
• - Development tools, development and
• target platforms, hardware, etc.
• Requirements changes during the entire
  development process

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Waterfall model fitness
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The waterfall model with prototyping
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V Model
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How to reduce cycle time?
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The incremental and iterative models
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Evolutionary development - characteristics

• Problems
• - Lack of process visibility
• - Systems are often poorly structured
• Applicability
• - For small or medium-size interactive systems
• - For parts of large systems (e.g. the user
  interface)
• - For short-lifetime systems

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The Spiral Model (88)