Abstract
The paper presents the process of taking global decisions on the basis of the knowledge of local decision systems involving the mutually complementary observations of objects which can be mutually contradictory. The authors suggest the organization of local decision systems into a multi-agent system with a hierarchical structure. The structure of multi-agent systems and the theoretical aspects of the organization of the system are presented. A density-based algorithm has been used in the process of taking global decisions. Furthermore the paper presents the results of experiments conducted using realistic data.