Abstract
Especially during the design and tuning of active rules, it is possible that rule execution enters an endless loop, where rules “cascade” by triggering each other indefinitely, so that their processing does not terminate. Commercial systems detect this situation in a simple way, by keeping counters on the number or depth of cascading rules, and suspending an execution when the counters exceed given thresholds. However, the setting of these counters is quite critical: too low thresholds may cause the halting of rule processing in absence of loops, too high thresholds may reveal a loop only after an expensive processing. In this paper, we propose a technique for revealing loops, which is based on recognizing that a given situation has already occurred in the past and therefore will occur an infinite number of times in the future. We exploit this property to develop cycle monitors, which check at run time that critical rule sequences, detected at compile time, do not repeat forever. We describe the run-time monitoring environment of Chimera, an active DBMS prototype currently under development at the Politecnico di Milano, and we illustrate with a concrete applicative example the results obtained with the cycle monitoring technique.
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Baralis, E., Ceri, S. & Paraboschi, S. Debugging and Run-time Monitoring of Active Rules. Journal of Systems Integration 7, 327–347 (1997). https://doi.org/10.1023/A:1008283421564
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DOI: https://doi.org/10.1023/A:1008283421564