This talk addresses the problem of how to maintain efficient reactive and pro-active behavior for continuous queries and notifications in moving object databases (MOD). Unlike traditional applications where queries are instantaneous, many queries of interest in MOD are continuous in nature and require constant re-evaluation over the history of the objects. We assume that that the motion of objects is represented by a trajectory, which consists of a sequence of 3D points.
We address first the problem of handling event notification in conjunction with dynamic topological predicates, such moving along and moving towards. We present efficient algorithmic solutions to handle these predicates based on computational geometry. We then show that traditional triggers are inadequate for handling the reactive behavior of these topological predicates since they repeatedly evaluate the conditions on the entire past trajectory.
Next, we introduce a new paradigm for expressing reactive behavior in distributed environments in which data continuously changes over time and which allows users to explicitly specify how the triggers should be (self) imodified. We call this paradigm Evolving and Context-Aware Event Condition Action (ECA) 2. Our model combines reactive behavior with proactive impact by modifying dynamically the evernt/conditions and actions monitored. Since both the monitored event and the condition part of the trigger can be continuous in nature, we introduce the concept of metatriggers to coordinate the detection of events and the evaluation of conditions. We conclude by discussing a high-level specification language for our triggers which allows for hypothetical reasoning.
Peter Scheuermann is a Professor of Electrical Engineering and Computer Science at Northwestern University. He has held visiting professor positions with the Free University of Amsterdam, the University of Hamburg and the Swiss Federal Institute of Technology, Zurich. During 1997-1998 he served as Program Director for Operating Systems at the NSF.. Dr. Scheuermann has served on the editorial board of the Communications of ACM, The VLB Journal and IEEE Transactions on Knowledge and Data Engineering. His current research interests are in parallel and distributed database systems, mobile computing, spatial databases and data mining. He has published more than 100 journal and conference papers. Peter Scheuermann is a Fellow of IEEE.