A Spiral Model of Software Development and Enhancement

1
A Spiral Model of Software Development and
Enhancement

• Barry Boehm
• Computer, May 1988
• text pp34-45

2
Software Process Model

• The primary functions of a software process
  model are to determine the order of the stages
  involved in software development and evolution
  and to establish the transition criteria for
  progressing from one stage to the next.

3
Who discovered the waterfall model?

• A. Royce in 1970
• B. Boehm in 1988
• C. Fred Waterfall in 1950
• D. It always existed, someone just named it in
  1966
• E. Every other discipline knew about it long ago

4
Advice

• Use a life-cycle development model to manage
  software development
• The stages become milestones to mark progress

5
Question

• How do you decide whether a stage is complete?
• A. The manager says it is complete
• B. The team is ready to go on to the next stage
• C. The team votes on whether it is complete

6
TRWs Ada Process Model for Incremental
Development of Large Software Systems

• Walker Royce
• 12th ICSE 1990
• text pp46-55

7
Interesting Approach

• Incremental development
• Used Ada as spec language as well as
  implementation
• Using stubs and drivers to execute partially
  implemented systems

8
Software Process

• Software Processes
• are software, too
• Leon Osterweil (1987)

9
software process
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Definition

• A process model is a description of the
  significant aspects of the tasks that are
  accomplished during the development of software,
  including the artifacts produced, the agents
  involved in the activities, and the relationships
  between these entities.

11
Rules for PM diagrams

• Every process must use one or more artifacts and
  must produce one or more artifacts.
• There must be an artifact between two consecutive
  processes.

12
Testing Fragment

• The test designer builds test cases using the
  source code and the documents. The output is a
  set of tests
• The test team does testing using the tests from
  the test designer and the source code producing a
  test report

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Example Fragment
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Example - testing

• shows who is responsible for what tasks
• shows what information is necessary for a task
• shows what is produced by a task
• shows sequences and dependencies of tasks

15
PM Notations

• Many possible notations
• functional diagrams
• state diagrams
• petri models
• textual descriptions
• programming languages

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PM - petri net
doc
source
designer
build t c
test team
tests
testing
test report
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Entities in Process Models

• Activities/Tasks
• Information
• Artifacts (Products)
• Knowledge
• Agents
• People, Positions, Roles
• Constraints

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Control Decisions

• Some PM show control in terms of decisions

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Example Fragment with Decision
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L3aS20 Group Task

• Create a process model for a cooking-dinner task.
  
• Work in groups of 2-4 only.
• Turn in at beginning of 2nd hour.