Rewriting-based Check of Chase Termination

The Chase is a fixpoint algorithm enforcing satisfaction of data dependencies (also called constraints) in databases. It has been proposed more than thirty years ago [2,18] and has seen a revival of interest in recent years in both database theory and practical applications. Indeed, the availability of data coming from different sources easily results in inconsistent or incomplete data (i.e., data not satisfying data dependencies) and, therefore, techniques for fixing inconsistencies are crucial [1,3,5,7,8,13,17]. The chase algorithm is used, directly or indirectly, on an everyday basis by people who design databases, and it is used in commercial systems to reason about the consistency and correctness of a data design. New applications of the chase in meta-data management, ontological reasoning, data exchange, data cleaning, and query optimization have been proposed as well [6,9]. The chase algorithm solves possible violations of constraints by inserting new tuples, possibly containing null values [4]. The following example shows a case where a given database does not satisfy a set of tuple generating dependencies (TGDs) and the application of the chase algorithm produces a new consistent database by adding tuples with nulls.