Software Reliability Growth

1
Software Reliability Growth
2
Three Questions Frequently Asked Just Prior to
Release

1. Is this version of software ready for release
   (however ready is being defined)?
2. How much additional effort is required to release
   it?
3. When will it be ready for release?

3
To Answer the Above Questions You Need a Software
Reliability Growth Model

• You can develop a reliability goal.
• Then track progress toward that goal.
• Based on data collected during software
  validation testing

4
Software Reliability Definitions

• Software Reliability The probability of
  failure-free operation of a computer program for
  a specified period of time operation in a
  specified environment.
• Reliability Growth The improvement in software
  reliability that results from correcting faults
  in the software.

5
Software Reliability Definitions (Contd)

• Software Availability The expected fraction of
  time during which the software functions
  acceptably.
• Fault A defect (or bug) in the software that
  causes a software failure.
• Failure a departure of the softwares operation
  from user requirements.

6
Software Reliability Definitions (Contd)

• Failure Intensity The number of failures
  occurring in a given time period.
• MTTF The average value of the next failure
  interval

7
The Test-Analyze-Fix Process
8
Reliability Growth Modeling

• Having a robust model can help management
• Make decisions regarding testing
• Decide when it is appropriate to make a release
• Determine what levels of support may be needed
  after release

9
Objectives of Modeling

• Measure and predict software reliability in terms
  of its mean time to failure (MTTF)
• Determine optimal time to stop testing and
  release software
• Provide data for making tradeoffs between test
  time, reliability, cost, and performance goals
• Define realistic software reliability goals

10
Characteristics of a Good Software Reliability
Model

• It predicts future failure behavior
• It computes meaningful results
• It is simple, widely applicable, and based on
  sound assumptions

11
Software Reliability Growth Model