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A lower bound on the number of opinions needed for fault-tolerant decentralized run-time monitoring

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Abstract

Runtime verification aims at extracting information from a running system, and using it to detect and possibly react to behaviors violating a given correctness property. Decentralized runtime verification involves a set of monitors observing the behavior of the underlying system. When the monitors themselves can fail, and communication among them is unreliable, it is unavoidable that the monitors may have different views of the system’s state and hence that they emit different opinions about its correctness at runtime. It is known that few correctness properties can be monitored in such a setting, when the set of opinions is the set {True, False}. In this paper, we initiate the investigation of decentralized fault-tolerant runtime monitoring under an arbitrary set of opinions. Specifically, we characterize the size of the opinion set required for monitoring a given correctness property in a decentralized manner. It turns out that the key factor impacting this size is the maximum number of times the monitored property can change its truth value over all executions of the monitors. Our lower bound is independent of the way the set of opinions returned by the monitors is globally interpreted, and it holds even when verifying a static system. Moreover, our lower bound is tight in the sense that we design a distributed protocol enabling any given set of monitors to verify any given correctness property on static systems, using as many different opinions as the one given by our lower bound.

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Notes

  1. In the case of chromatic manifolds, our definition is equivalent to the usual definition of orientation in topology textbooks (see e.g., Bracho and Montejano 1987).

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Acknowledgements

We thank the anonymous referee for carefully reviewing the paper.

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Correspondence to Corentin Travers.

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All authors are supported in part by the CONACYT-CNRS ECOS Nord M12M01 research Grant.

P. Fraigniaud: Additional support from ANR project DESCARTES, and from INRIA project GANG.

S. Rajsbaum: Additional support from UNAM-PAPIIT and LAISLA.

C. Travers: Additional support from ANR project DESCARTES.

An extended abstract of this paper was presented at the 14th International Conference on Runtime Verification (RV), September 22–25, 2014, Toronto, Canada, whose proceedings appeared in Springer’s LNCS 8734.

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Fraigniaud, P., Rajsbaum, S. & Travers, C. A lower bound on the number of opinions needed for fault-tolerant decentralized run-time monitoring. J Appl. and Comput. Topology 4, 141–179 (2020). https://doi.org/10.1007/s41468-019-00047-6

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  • DOI: https://doi.org/10.1007/s41468-019-00047-6

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