INTROSE Introduction to Software Engineering

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INTROSE Introduction to Software Engineering
Software Definitions, Myths, and Process Models

• Raymund Sison, PhD
• College of Computer Studies
• De La Salle University
• sisonr_at_dlsu.edu.ph

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Question

• What is software?

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What is software?

• Software is a set (configuration) of computer
  programs and associated documentation and data.
• (Sommerville, 2001)

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What is software?

• Software can be
• System software
• Business software
• Engineering and scientific software
• Embedded software
• Personal productivity software
• Web-based software (Web apps)
• Artificial intelligence software

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What is software?

• Software
• Is engineered, not manufactured
• Doesnt wear out, but it does deteriorate (see
  next slide)
• Is still usually custom-built, though reusable
  components that are reliable and easy to use are
  steadily increasing

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Wear vs. Deterioration
From (Pressman, 2001)
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Software Myths

• Management myths
• All that my people need to develop good software
  are state-of-the-art computers.
• All that my people need to develop good software
  are documented in a book of standards and
  procedures.
• If we get behind schedule, we simply add more
  programmers.
• If I decide to outsource a software development
  project to another firm, I can just relax and let
  that firm do it.

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Software Myths

• Customer myths
• A general statement of objectives is sufficient
  to begin writing programs we can fill in the
  details later.
• Project requirements continually change, but
  change can be easily accommodated because
  software is flexible.

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Software Myths

• Practitioners myths
• Once we write the program and get it to work, our
  job is done.
• Until I get the program running, I have no way
  of assessing its quality.
• The only deliverable work product for a
  successful project is the working program.
• Software engineering will make us create
  voluminous and unnecessary documentation and will
  invariably slow us down.

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What is software engineering?

• Software engineering is the production of quality
  software (and the study of approaches to all
  aspects thereof).

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Software Process

• A software process is a set of activities that
  produce a software product.

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Generic Software Activities

• Specification
• Planning
• Requirements analysis
• Development
• Design
• Coding
• Verification and validation
• Maintenance (a.k.a. Evolution)
• Correction
• Adaptation
• Enhancement

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Support Software Activities

• Complementing the generic software activities are
  the following umbrella activities
• Software project tracking and control
• Formal technical reviews
• Software quality assurance
• Software configuration management
• Document preparation and production
• Measurement
• Risk management

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Software Process Model

• A software process model is a simplified
  description of a software process.

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Some Software Process Models

• Some software process models
• Linear
• Iterative
• Evolutionary
• Incremental
• Spiral
• Unified Process
• Agile
• Formal

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Some Software Process Models

1. Linear (a.k.a. Waterfall) oldest and most
   widely used

From (Sommerville, 2001)
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Some Software Process Models

• Drawbacks of the Waterfall model
• It is often difficult for customers to state all
  requirements explicitly.
• Accommodating change is difficult in Waterfall.
• Therefore this model is appropriate only when
  requirements are well understood.
• The customer must have patience.

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Some Software Process Models

1. Evolutionary (Iterative)

From (Pressman, 2001)
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Some Software Process Models

1. Incremental (Iterative)

From (Pressman, 2001)
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Some Software Process Models

• Spiral (Iterative)

From (Boehm, 1988)
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Some Software Process Models

1. Unified Process (Iterative)

From (Jacobson, Booch Rumbaugh, 1999)
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Some Software Process Models

• Agile, e.g.,Scrum (Iterative)

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Some Software Process Models

• XP Sidebar (from ADVANSE slides)

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Some Software Process Models

• Other generic process models
• Formal methods used when a mathematical
  specification is to be developed
• Component assembly used when reuse is a
  development objective

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Impact of Process Model

• If appropriate,
• can improve
• development speed
• quality
• tracking control
• client relations
• can minimize
• overhead
• risk exposure

• If inappropriate,
• can make some work
• slow
• unnecessary
• redundant
• frustrating

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Brooks No Silver Bullet

• Software engineering involves
• Essential tasks
• The fashioning of the complex conceptual
  structures that compose the abstract software
  entity
• Accidental tasks
• The representation of these abstract entities in
  programming languages and the mapping of these
  onto machine languages within space and speed
  constraints

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Brooks No Silver Bullet

• For accidental tasks, increase productivity
  through automation
• For essential tasks, increase productivity
  through
• Great designers
• Rapid prototyping
• Evolutionary development
• Software reuse