Formal Failure Models

Formal safety analysis methods have gained a lot of importance during the last years. All these methods have in common, that they rely on a formal model of a system which describes desired, functional behavior as well as unwanted erroneous behavior correctly. Most of the time the formal models are created in an ad hoc manner. This is very error prone and therefore compromises the benefit of the following formal analysis. In this paper we present a systematic approach to formally model failure modes. The approach can be combined with most formal safety analysis. We apply the method to a real world case study: a radio-based railroad crossing. We illustrate the results by applying a formal safety analysis method on the model.