Exploiting equality generating dependencies in checking chase termination

Abstract

The chase is a well-known algorithm with a wide range of applications in data exchange, data cleaning, data integration, query optimization, and ontological reasoning. Since the chase evaluation might not terminate and it is undecidable whether it terminates, the problem of defining (decidable) sufficient conditions ensuring termination has received a great deal of interest in recent years. In this regard, several termination criteria have been proposed. One of the main weaknesses of current approaches is the limited analysis they perform on equality generating dependencies (EGDs). In this paper, we propose sufficient conditions ensuring that a set of dependencies has at least one terminating chase sequence. We propose novel criteria which are able to perform a more accurate analysis of EGDs. Specifically, we propose a new stratification criterion and an adornment algorithm. The latter can both be used as a termination criterion and be combined with current techniques to make them more effective, in that strictly more sets of dependencies are identified. Our techniques identify sets of dependencies that are not recognized by any of the current criteria.