The use of digital systems is on increase in nuclear industry in recent years. Therefore, the importance of system verification and validation (V/V) is more emphasized in view of the nuclear safety. There is, however, no generally applicable software design process and software failure model that is sufficiently accurate to enable reliability or safety predictions to be made for safety critical systems. In addition, until nearly a decade ago, there was a lack of emphasis on V/V in the earlier stages of software development, thus consequently heavy reliance was placed upon testing. Therefore, we have a lot of difficulty in performing V/V practically and effectively though there trends to be more emphasis upon introducing V/V activities earlier and throughout the software development process. In order to overcome the difficulty, many researchers have proposed various software V/V techniques and software quality control methods.
The main objective of this research is to construct an environment for V/V of safety critical software at the early development stages. The V/V environment consists of two V/V techniques and a V/V guideline. The two V/V techniques are software requirements analysis, software hazard analysis, and the V/V guideline is software safety classification. V/V techniques provide tools for performing V/V activities and V/V guideline offers facility to a V/V team.
The V/V environment tries to resolve the following weak points that the existing V/V techniques or V/V guidelines have:
- To integrate formal methods into traditional methods in one methodology.
- To formally analyze software hazards at the early development stage.
- To support quality control in a rigorous manner with a formal V/V guideline.
As V/V techniques, this study has proposed Combined Colored Petri Nets and Prototype Verification System (Combined CPN and PVS) and CPN based Software Fault Tree Analysis (CPN-SFTA) as requirements analysis method and hazard analysis method, respec...