Ensuring Consistency of Conditional Graph Grammars -a Constructive Approach

Consistency conditions describe basic properties of graphs as e.g. the existence or uniqueness of certain elements. A graph grammar is consistent if the start graph satisses the consistency condition and the rules preserve this property. We propose a general construction that transforms global consistency conditions into preconditions for individual rules. A so-constructed rule is applicable to a consistent graph if and only if the derived graph is consistent, too. The relevance of this result is motivated by an example speciication of a safety-critical system that is, a roundabout .