Shape Sensitive Geometric Monitoring

An important problem in distributed, dynamic databases is to continuously monitor the value of a function defined on the nodes, and check that it satisfies some threshold constraint. We introduce a monitoring method, based on a geometric interpretation of the problem, which enables to define local constraints at the nodes. It is guaranteed that as long as none of these constraints is violated, the value of the function did not cross the threshold. We generalize previous work on geometric monitoring, and solve two problems which seriously hampered its performance: as opposed to the constraints used so far, which depend only on the current values of the local data, here we incorporate their temporal behavior. Also, the new constraints are tailored to the geometric properties of the specific monitored function. In addition, we extend the concept of safe zones for the monitoring problem, and show that previous work on geometric monitoring is a special case of the proposed extension. Experimental results on real data reveal that the new approach reduces communication by up to three orders of magnitude in comparison to existing approaches, and considerably narrows the gap between achievable results and a newly defined lower bound on communication complexity.