|4.47 Method Category "Reliability Models" (RELM)|
/Goel, 1985/ can be used as a general description.
A Reliability Model is applied for the identification, the compression and the proof of reliability requirements. Based on the user-oriented requirements and environment, the system is to be represented by the model either complete or adaptive.
The Reliability Models is not only to inform about achieving the user-oriented quality goals but also about criteria in connection with these goals, as well as about the interim goals to be achieved (reliability increase) and the influence of technical changes.
The principle of the method is to develop a model that makes it possible to obtain information about the functions of a software/a system and the corresponding reliability state.
In order to measure the reliability state, different reliability characteristics are applied. The characteristics most frequently applied are:
The characteristic "Mean Time between Failures" is based on measuring the time interval between the occurrence of failure n and the occurrence of failure n+1. In the case where an acceptable value has been reached for the time interval, both development and quality assurance can be finished.
The characteristic "Failure Rate" counts or estimates the number of failures during the predefined interval. If the cumulative number of occurred failures has reached an acceptable (low) number during the time interval, both development and quality assurance can be finished.
The characteristic "Estimated Number of Faults Remaining" estimates the number of faults remaining in the program. If this number is acceptable, both development and quality assurance can be finished.
Realization and application of a reliability model are closely connected with the measuring process for the reliability state.
|4.1||SD1.3 - Definition of Criticality and Quality Requirements||Method RELM is applied for the definition of requirements for the reliability of system functions. It completely covers subproduct User Requirements.Quality Requirements, but only with regard to the reliability.|
|4.2||SD3.4 - Definition of Requirements for the Quality of the SW/HS Unit||Method RELM is applied to define the requirements for the reliability of system functions. It completely covers subproduct 5.x.4.3.Technical Requirements.Technical Requirements for Other Quality Characteristics, but only with regard to reliability.|
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