Like most systems, automotive software systems evolve due to many reasons including adding, removing or modifying features, fixing bugs, or improving system quality. In this context, safety cases, used to demonstrate that a system satisfies predefined safety requirements, often dictated by a standard such as ISO 26262, need to co-evolve. A necessary step is performing an impact assessment to identify how changes in the system affect the safety case. In previous work, we introduced a generic model-based impact assessment approach, that, while sound, was not particularly precise. In this work, we show how exploiting knowledge about system changes, the particular safety case language, and the standard can increase the precision of the impact assessment, reducing any unnecessary revision work required by a safety engineer. We present six precision improvement techniques illustrated on a GSN safety case used with ISO 26262.
