Safe Control Systems (SaCS) pattern language for the develop-
ment of conceptual safety designs. By a conceptual safety design we mean an early stage specification of system requirements, system design, and safety case for a safety critical system. The SaCS pattern language may express basic patterns on different aspects of relevance for conceptual safety designs. SaCS may also be used to combine basic patterns into composite patterns. A composite pattern may be instantiated into a conceptual safety design. A framework for evaluating modelling languages is used to conduct the evaluation. The quality of a language is within the framework expressed by six appropriateness factors. A set of requirements is associated with each appropriateness factor.
The extent to which these requirements are fulfilled are used to judge the quality. We discuss the fulfilment of the requirements formulated for the SaCS language on the basis of the theoretical, technical, and practical considerations that were taken into account and shaped the SaCS language.