Stop the Chase

The chase procedure, an algorithm proposed 25+ years ago to fix constraint violations in database instances, has been successfully applied in a variety of contexts, such as query optimization, data exchange, and data integration. Its practicability, however, is limited by the fact that – for an arbitrary set of constraints – it might not terminate; even worse, chase termination is an undecidable problem in general. In response, the database community has proposed sufficient restrictions on top of the constraints that guarantee chase termination on any database instance. In this paper, we propose a novel sufficient termination condition, called inductive restriction, which strictly generalizes previous conditions, but can be checked as efficiently. Furthermore, we motivate and study the problem of data-dependent chase termination and, as a key result, present sufficient termination conditions w.r.t. fixed instances. They are strictly more general than inductive restriction and might guarantee termination although the chase does not terminate in the general case.