Abstract. We propose a framework for model-based diagnosis of systems with mobility and variable topologies, modelled as graph transformation systems. Generally speaking, model-based diagnosis is aimed at constructing explanations of observed faulty behaviours on the basis of a given model of the system. Since the number of possible explanations may be huge we exploit the unfolding as a compact data structure to store them, along the lines of previous work dealing with Petri net models. Given a model of a system and an observation, the explanations can be constructed by unfolding the model constrained by the observation, and then removing incomplete explanations in a pruning phase. The theory is formalised in a general categorical setting: constraining the system by the observation corresponds to taking a product in the chosen category of graph grammars, so that the correctness of the procedure can be proved by using the fact that the unfolding is a right adjoint and thus it preserves products. The theory thus should be easily applicable to a wide class of system models, including graph grammars and Petri nets. 1

Functorial models for contextual pre-nets

Graph Types" and "Updatable Graph Views".

This paper describes a multirelation semantics for a fragment of the Extended Entity-Relationship schemata formalism based on the bicategorical definition of multirelations. The approach we follow is elementary---we try to introduce as few notions as possible. We claim that bicategorical algebra handles gracefully multirelations and their operations, and that multirelations are essential in a number of applications; moreover, the bicategorical composition of multirelations turns out to correspond to natural joins. From the formal semantics we derive an algorithm that can establish statically the possibility of building parallel ownership paths of weak entities. The ideas described in this paper have been implemented in a free tool, ERW, which lets users edit sets and multirelations instantiating an EER schema via a sophisticated web interface.