Abstract. Graph transformation systems are a general specification language for systems with dynamically changing topologies, such as mobile and distributed systems. We propose a counterexample-guided abstraction refinement technique which is based on the over-approximation of graph transformation systems (gts) by Petri nets. We show that a spurious counterexample is caused by merging nodes during the approximation. We present a technique for identifying these merged nodes and splitting them using abstraction refinement, which removes the spurious run. The technique has been implemented in the Augur tool and experimental results are discussed. 1

† Funded by the Dutch NWO project GRASLAND (Grant nr. 612.063.408) 1 2

Aspect-oriented programming (AOP) aims at managing crosscutting concerns at the programming language level. AOP is basically an evolution technique that may be used to augment a system with a new concern considered orthogonal to the others. The augmentation is applied automatically to a code base and is described with respect to a model of it. With AspectJ-like approaches this model has to be described as a set of join points, a solution that is in most cases too low level. Programmers should instead have the power of abstracting from the code base the model they prefer. Then, the augmentations described with respect to this specific model can be woven into the original system. Since the model introduced is specific to the concern the designer is trying to tackle, it may explicitly express design decisions,

Abstract. Refactoring of information systems is hard, for two reasons. On the one hand, large databases exist which have to be adjusted. On the other hand, many programs access that data. These programs all have to be migrated in a consistent manner such that their semantics does not change. It cannot be relied upon, however, that no running processes exist during such a migration. Consequently, a refactoring of an information system needs to take care of the migration of data, programs, and processes. This paper introduces a model for complete object-oriented systems, describing the schema level with classes, associations, operations, and inheritance as well as the instance level with objects, links, methods, and messages. Methods are expressed by special double-pushout graph transformations. Homomorphisms are used for the typing of the instance level as well as for the description of refactorings which specify the addition, folding, and unfolding of schema elements. Finally, a categorial framework is presented which allows to derive instance migrations from schema transformations in such a way that programs and processes to the old schema are correctly migrated into programs and processes to the new schema. 1