section8 - 8.0 RELIABILITY GROWTH AND DEMONSTRATION TESTING...

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8-1 8.0 RELIABILITY GROWTH AND DEMONSTRATION TESTING Reliability growth testing is performed to assess current reliability, identify and eliminate faults, and forecast future reliability. The reliability figures are compared with intermediate reliability objectives to measure progress so that resources can be directed to achieve the reliability goals in a timely and cost- effective manner. Whenever a failure occurs, corrective action is undertaken to remove the cause. For hardware, growth testing is the process of testing the equipment under both natural and induced environmental conditions to discover latent failure modes and mechanisms to ensure that all performance, design, and environmental problems have been resolved. Reliability demonstration is employed toward the end of the growth testing period to verify that a specific reliability level has been achieved. During a demonstration test, the software code is frozen, just as it would be in field use. Software growth testing and demonstration testing should be performed under the same conditions as field use. That is, the environment in which the software executes must emulate what the software will experience in the field, and environmental conditions must be maintained throughout the test period. 8.1 Software Operational Profile . The software execution environment includes the hardware platform, the operating system software, the system generation parameters, the workload, and the operational profile. The operational profile is described in detail in Section 9. Software reliability testing is based on selecting input states from an input space. An input state is a set of input variable values for a particular run. Each input variable has a declared data type (a range and ordering of permissible values). The set of all possible input states for a program is the input space. Each input state is a point in the input space. An operational profile is a function p that associates a probability p(i) with each point i in an input space I. Since the points in the input space are mutually exclusive and exhaustive, all the probabilities must add up to one: Example: To illustrate the operational profile concept, consider a program with three input variables. Each is of data type Boolean, meaning that it has two possible values: TRUE or FALSE. The input space has eight points: (FALSE,FALSE,FALSE), (FALSE,FALSE,TRUE), (FALSE,TRUE,FALSE), (FALSE,TRUE,TRUE), (TRUE,FALSE,FALSE), (TRUE,FALSE,TRUE), (TRUE,TRUE,FALSE), (TRUE,TRUE,TRUE). iI p(i) = 1 (8.1)
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8-2 Letting T stand for TRUE and F for FALSE, an operational profile for the program might look like: The distribution of input states is thus established by the operational profile. This is an explicit profile, as described in Section 9. During growth and demonstration testing the operational profile must be kept stationary (i.e., the p(i)’s should not change). The input states chosen for test cases should form a random sample from the input state in accordance with the distribution of input states that the operational profile specifies.
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section8 - 8.0 RELIABILITY GROWTH AND DEMONSTRATION TESTING...

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