Monitoring the Behaviour of Distributed Systems

ISSN 1476-2986 Monitoring the behaviour of computing systems is an important task. In active database systems, a detected system behaviour leads to the triggering of an ECA (event-condition-action) rule. ECA rules are employed for supporting database man-agement system functions as well as external applications. Although distributed database systems are becoming more commonplace, active database research has to date focussed on centralised systems. In distributed debugging systems, a de-tected system behaviour is compared with the expected system behaviour. Differ-ences illustrate erroneous behaviour. In both application areas, system behaviours are specified in terms of events: primitive events represent elementary occurrences and composite events represent complex occurrence patterns. At system runtime, specified primitive and composite events are monitored and event occurrences are detected. However, in active database systems events are monitored in terms of physical time and in distributed debugging systems events are monitored in term