Heterogeneous information systems are inevitable today but make an integration to cover business requirements difficult due to their non-cooperative behaviour. The paper summarizes the results of the author PhD thesis (submitted at the Technical University of Darmstadt) and presents its main conceptual contribution,viz. a framework to describe the conflict between global consistency and autonomy in database federations.

The term consistency is defined in a more generalized manner than traditionally in centralized homogeneous database systems. Our approach bases on the idea to model local data of existing systems by active objects which act as placeholders in a mediator system. ECA (Event-Condition-Action) rules are applied as expressive means for the specification of global integrity constraints. The practical use of the approach is proven by the prototypical implementation of an active object-oriented mediator as an extension of a commercially available system. Its concept and architecture is presented. Thereby, solutions for the detection of local events are demonstrated with the example of relational database systems.

Thomas Kudrass