The software process

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The software process

• A structured set of activities required to
  develop a software system
• Specification
• Design
• Implementation
• Testing (Validation)
• Installation (Release)
• Maintenance (Evolution)
• A software process model is an abstract
  representation of a process. It presents a
  description of a process from some particular
  perspective

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Software process models

• Waterfall
• Evolutionary/prototyping development
• Reuse-based development
• Incremental development
• Spiral development
• Extreme programming
• Rational Unified Process
• Object oriented model (fountain model)

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Waterfall model
Feedback loops
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Waterfall Good and Bad

• First published model
• Good
• Appropriate when the requirements are
  well-understood
• Simple, well-understood, easy to follow
• It includes feedback loops for maintenance
• Document driven model makes maintenance easier
• Bad
• Unrealistic for new product development
• Inflexible partitioning of the project into
  distinct stages
• Users feedback are late. This makes it difficult
  to respond to changing customer requirements

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Evolutionary development
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Evolutionary Good and Bad

• Development of an initial implementation followed
  by refinements
• Good
• Starts with a well understood subset of
  requirements
• Best for exploratory work
• Meets immediate needs of customers
• Bad
• Poorly structured, unclear milestones
• Inappropriate for very large projects
• Special skills (e.g. in languages for rapid
  prototyping) may be required

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Prototyping model

• Used to determine users needs
• No validation, few functionality is implemented
• Good
• Good to determine requirements
• Better specification expected
• Gives early feedback to user and developer
• Good for client to experiment and interact with
  it
• Bad
• User may see it as a working product
• Developers are asked to compromise implementation
• Software quality has not yet being considered
• Inappropriate programming language may have been
  used

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Reuse Good and Bad

• Based on systematic reuse where systems are
  integrated from existing components or COTS
  (Commercial-off-the-shelf) systems
• Good
• Fastest development cycle
• Low risk
• Bad
• May not exactly meet requirements
• Components may not be available

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Reuse-oriented development
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Incremental development Good and Bad

• Develop to completion portions of specs at a time
• Highest priority requirements included earlier
• Good
• Customer gets soon an operational product
• Lower risks of overall project failure (no large
  capital outlay)
• Requirements are frozen for each increment
• Customer could stop the next increment
• Bad
• Unnecessary if requirements and design are well
  understood
• No clear distinction between maintenance and
  development
• Complete set of requirements is required before
  first build

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Incremental development
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Extreme programming

• New approach to development based on the
  development and delivery of very small increments
  of functionality
• Main features
• Emphasis on getting software to work
• Relaxed requirements and design
• Short release cycles
• Comprehensive unit tests
• Pairwise programming
• Adding what is needed for the current task
• User involvement

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Spiral development

• Process is represented as a spiral rather than as
  a sequence of activities with backtracking
• Each loop in the spiral represents a phase in the
  process.
• No fixed phases such as specification or design -
  loops in the spiral are chosen depending on what
  is required
• Risks are explicitly assessed and resolved
  throughout the process

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Spiral model of the software process
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Spiral Good and Bad

• Good
• High likelihood of success (due to risk
  assessment and planning on each phase)
• It allows other process model in any of the
  phases
• Bad
• Time consuming

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Object oriented Model

• OO development is highly iterative
• Fountain model stresses the overlap of tasks
• Like the water in a fountain
• Software components are created, modified,
  discarded, or reused in successive phases
• Main advantages
• Requirements do not have to be frozen ? they
  evolve
• Phase overlap leads to parallel implementation
• Main disadvantages
• It may lead to an undisciplined implementation
• Phase overlapping may lead to low quality
  components

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Fountain Model
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Software specification
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Software design
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Implementation and debugging

• Translating a design into a program and removing
  errors from that program
• Programming is a personal activity - there is no
  standard model but lots of coding templates
• Programmers carry out some program testing to
  discover faults in the program and remove these
  faults in the debugging process

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Software testing (validation)
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Software maintenance (evolution)
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Automated process support (CASE)

• Computer-aided software engineering (CASE) is
  software to support software development and
  evolution processes
• Improve productivity and management of
  development process
• It does not support team interaction
• Activity automation
• Graphical editors for system model development
• Data dictionary to manage design entities
• Graphical UI builder for user interface
  construction
• Debuggers to support program fault finding
• Automated translators to generate new versions of
  a program

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CASE tool classification