Consistent detection of global predicates
PADD '91 Proceedings of the 1991 ACM/ONR workshop on Parallel and distributed debugging
Temporal interactions of intervals in distributed systems
Journal of Computer and System Sciences
Detection of Strong Unstable Predicates in Distributed Programs
IEEE Transactions on Parallel and Distributed Systems
Time, clocks, and the ordering of events in a distributed system
Communications of the ACM
Global predicates in rough real time
SPDP '95 Proceedings of the 7th IEEE Symposium on Parallel and Distributeed Processing
A Fine-Grained Modality Classification for Global Predicates
IEEE Transactions on Parallel and Distributed Systems
Causality-Based Predicate Detection across Space and Time
IEEE Transactions on Computers
Temporal Predicate Detection Using Synchronized Clocks
IEEE Transactions on Computers
Distributed Computing: Principles, Algorithms, and Systems
Distributed Computing: Principles, Algorithms, and Systems
Concurrent Event Detection for Asynchronous consistency checking of pervasive context
PERCOM '09 Proceedings of the 2009 IEEE International Conference on Pervasive Computing and Communications
Event ordering in pervasive sensor networks
PERCOM '09 Proceedings of the 2009 IEEE International Conference on Pervasive Computing and Communications
Immediate detection of predicates in pervasive environments
Proceedings of the 9th International Workshop on Adaptive and Reflective Middleware
Programming wireless sensor networks: Fundamental concepts and state of the art
ACM Computing Surveys (CSUR)
Composite event detection as a generic middleware extension
IEEE Network: The Magazine of Global Internetworking
Immediate detection of predicates in pervasive environments
Proceedings of the 9th International Workshop on Adaptive and Reflective Middleware
Immediate detection of predicates in pervasive environments
Journal of Parallel and Distributed Computing
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An important task in sensor networks is to sense locally to detect global properties that hold at some instant in physical time. We propose software logical clocks, called strobe clocks, that can be implemented by the middleware when synchronized physical clocks are not available or are too expensive in resource-constrained environments. Strobe clocks come in two flavors -- scalar and vector. Let n be the number of sensors and p be the upper bound on the number of relevant events sensed at a sensor. We propose an algorithm using vector strobes that can detect all occurrences of a conjunctive predicate in time O(n3p). The algorithm has some false negatives but this is the best achievable accuracy in the face of race conditions. We also present a variant algorithm using scalar strobes; it needs time O(n2p) but may also suffer from some false positives. We provide a characterization of the errors. Both algorithms can also detect relational predicates but with a greater chance of error. The message complexity of strobe clocks (scalar and vector) and both algorithms is O(np), which is the same as that of reporting each sensed event for detection of the predicate even with synchronized physical clocks.