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Active database systems enhance the functionality of traditional databases through the use of active rules or ‘triggers’. One of the principal analysis questions for such systems is that of termination—is it possible for the rules to recursively activate one another indefinitely, given an initial triggering event. In this paper, we study the decidability of the termination problem, our aim being to delimit the boundary between the decidable and the undecidable. We present results for two broad types of variations, variations in rule syntax and variations in meta level features. Within each of these, we identify members close to the boundary of (un)decidability and also look at the effect of combining members of each type. The maximal decidable class we present is capable of expressing some useful kinds of application requirements, such as checking and repairing inclusion constraints. The work is also interesting from a theoretical point of view, since the context is similar to the while query language and the dynamics gives an interesting contrast to Datalog with negation.


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