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Unformatted text preview: 4-1 4.0 OVERVIEW Reliability assurance of combined hardware and software systems requires implementation of a thorough, integrated set of reliability modeling, allocation, prediction, estimation and test tasks. These tasks allow on-going evaluation of the reliability of system, subsystem and lower-tier designs. The results of these analyses are used to assess the relative merit of competing design alternatives, to evaluate the reliability progress of the design program, and to measure the final, achieved product reliability through demonstration testing. At each step in the design-evaluate-design process, the metrics used to predict product reliability provide a mechanism for a total quality management system to provide ongoing control and refinement of the design process. Table 4-1 provides a summary of the analysis and test tasks for both hardware and software that provide reliability goals, predictions, and assessments. Figure 4-1 illustrates an overview of the interrelationships between these tasks. 4.1 System Reliability Prediction and Estimation Program. The reliability prediction and estimation program for systems which combine both hardware and software elements must be composed of a complementary set of hardware and software tasks for reliability modeling, reliability allocation, reliability prediction, reliability growth testing, and reliability qualification testing. Each of the complementary tasks should support system level tasks which combine the results of the individual hardware and software tasks and allow assessment of the overall system reliability performance. 4.1.1 System Modeling. System modeling provides a functional representation of the system under analysis. An accurate system model provides a mechanism for all reliability analyses performed.System reliability modeling for hardware and software system is an evaluation of the dependency between system services and the various hardware elements and their associated software processes. The system model is developed as an iterative process of decomposing the dependencies within the various system structural elements. As appropriate to the size and complexity of the system being analyzed, the system is first decomposed into a reliability block diagram showing the dependency between the subsystems and the system services required for a given mission or mode of operation. 4-2 TABLE 4-1. Reliability Prediction and Estimation TasksPREDICTION AND ESTIMATION PROGRAM TASK APPLIES TO REMARKS HW SW Operational Profile Development X X Operational profile development is represented in Sections 6 and 9 of this notebook. Reliability Modeling X X Reliability modeling for HW/SW systems is presented in Section 5. of this notebook Reliability Allocation X X SW Allocation Procedures are provided in 6 of this notebook Reliability Prediction X X Procedures for SW reliability prediction at each phase of SW development are given in 7 Environmental Stress Screening X -A SW equivalent of HW stress screening...
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- Spring '11
- Software engineering, software system, software reliability