CoSent: A Cooperative Sentinel for Database Systems

Active database systems have received increasing interest from both research and industrial communities. However, trigger conditions in the active rules are often dif-cult to specify, especially as the events and/or conditions complexities increase. To remedy this problem, we propose an active database system that supports rules with conceptual terms, approximate operators, and complex events. The conceptual terms and approximate operators are user and context sensitive. By introducing these high-level constructs, we not only simplify the rule speciication process, but also increase the rule expressiveness. Knowledge-based relaxation techniques are used for rule speciica-tion and relaxation. High-level concepts and approximate operators used in rules are rst relaxed into low-level active rules by using a tree-type knowledge structure called Type Abstraction Hierarchy which can be generated automatically from the database using clustering algorithms. The low-level rules are decomposed into a set of database triggers, which are then submitted into commercial active relational databases for simple trigger processing. Thus, our proposed high-level active database system supports 1 complex event detection without modiication of the underlying database systems. This is in contrast to some of the research work on complex event detection that requires modiication of the underlying database systems. A new, more exible event condition evaluation scheme is proposed for processing complex conditioned events. Such an evaluation scheme also ts naturally into the distributed environment for detecting complex conditioned events that occur at diierent sites to cause a joint action. The proposed active database system with high-level rule processing and complex event detection has been implemented at UCLA. The system operates on top of commercial relational databases that demonstrates the feasibility of high-level rule processing and complex events detection.