There are many industrial products in our life, and the actions of those products are controlled by embedded control software (ECSW). Recently, many troubles have been caused by ECSW. To avoid those troubles, it is necessary to clarify the causes of the troubles and take countermeasures. However, the results of those tasks depend on the skills of the analyst. This paper proposes an analytic method that clarifies the causes of troubles by applying fault tree analysis (FTA) to the ECSW. The characteristics of the proposed method are as follows: Preparation of fault tree templates (FTTs) corresponding to instructions of the ECSW, and definition of the FT development rules by combining FTTs according to the back-tracing of the instruction execution process. By complying with the proposed method strictly, when an analyst who has studied computer science and safety engineering for 2–3 years conducts FTA, the analyst can obtain an appropriate result of FTA. This indicates that the safety level of ECSW will improve. As a result of applying the proposed method to existing ECSWs, we find that we can obtain the result of FTA at the appropriate level.

No abstract

In this study, we proposed a method to improve the safety level of control software (CSW) by managing the CSW’s design information and safety analysis results, and combining failure mode and effects analysis (FMEA) and fault tree analysis (FTA). Here, the CSW is developed using structured analysis and design methodology. In the upper stage of the CSW’s development process, as the input of the preliminary design information (data flow diagrams (DFDs) and control flow diagrams (CFDs)), the causes of undesirable events of the CSW are clarified by FMEA, and the countermeasures are reflected in the preliminary design information. In the lower stage of the CSW’s development process, as the inputs of the detailed design information (DFDs and CFDs in the lower level) and programs, the causes of the specific undesirable event are clarified by FTA, and the countermeasures are reflected in the detailed design specifications and programs. The processes are repeated until the impact of undesirable events become the acceptable safety level. By applying the proposed method to the CSW installed into a communication control equipment on the space system, we clarified several undesirable events and adopted adequate countermeasures. Consequently, a safer CSW is developed by applying the proposed method.

No abstract

No abstract

No abstract

Changes of software requirements are inevitable during the development life cycle. Rather than avoiding the circumstance, it is easier to just accept it and find a way to anticipate those changes. This paper proposes a method to analyze the volatility of requirement by using the Quality Function Deployment (QFD) method and the introduced degree of volatility. Customer requirements are deployed to software functions and subsequently to architectural design elements. And then, after determining the potential for changes of the design elements, the degree of volatility of the software requirements is calculated. In this paper the method is described using a flow diagram and illustrated using a simple example, and is evaluated using a case study.

No abstract