Software architecture and safety

Safety critical systems are growing more complex. To keep these systems safe, methods and techniques are necessary to prevent accidents from happening. Earlier when the engineered systems were smaller and the possibility for large scale destruction was not there, we had the luxury of being in a position to learn from experience. Due to the catastrophes safety critical systems can cause today, we no longer have that luxury [11]. To solve this, methods such as HAZOP and FTA can be used. These methods require a good description of the system as input to give results. UML is a well known tool for describing software. Using UML use cases as input to HAZOP and the results from the HAZOP and UML class diagrams and sequence diagrams as input for a FTA analysis is a way of obtaining good information about the safety of the system. In this project a development of a safety critical prototype in LEGO Mindstorms is designed. The resulting FTA analysis of the design suggests that carrying out more iterations with analyses and redesign would be necessary to create a design that is safe enough for implementation of a safety critical prototype. Using UML use cases as input to HAZOP and the results of the analysis as input for FTA together with information from UML class diagrams and sequence diagram gave a reasonably good design after only one iteration.This indicates that the methods work well when used during these stages of the process.