Active database systems have been a hot research topic for quite some years now. However, while active functionality has been claimed for many systems, and notaions such as active objects or events are used in many research areas (even beyond database technology), it is not yet clear which functionallity a database management system must support in order to be legitimately considered as an active systewm. In this paper, we attempt to clarify the notion of active database management system as well as the functionality it has to support. We thereby distinguish mandatory features that are needed to quality as an active datavbase system, and desired features which are nice to have finally, we perform a classifications of active database systems and identify the requirements for an active database management system in order to be applicable in these application areas.