On chase termination beyond stratification

On Chase Termination Beyond Stratification

We study the termination problem of the chase algorithm, a central tool in various database problems such as the constraint implication problem, Conjunctive Query optimization, rewriting queries using views, data exchange, and data integration. The basic idea of the chase is, given a database instance and a set of constraints as input, to fix constraint violations in the database instance. It i...

Stratification-based Criteria for Checking Chase Termination

Several database areas such as data exchange and integration share the problem of fixing database instance violations with respect to a set of constraints. The chase algorithm solves such violations by inserting tuples and setting the value of nulls. Unfortunately, the chase algorithm may not terminate and the problem of deciding whether the chase process terminates is undecidable. Recently the...

On Conditional Chase Termination

Stratification Criteria and Rewriting Techniques for Checking Chase Termination

The Chase is a fixpoint algorithm enforcing satisfaction of data dependencies in databases. Its execution involves the insertion of tuples with possible null values and the changing of null values which can be made equal to constants or other null values. Since the chase fixpoint evaluation could be non-terminating, in recent years the problem know as chase termination has been investigated. It...

Termination of oblivious chase is undecidable

We show that all–instances termination of chase is undecidable. More precisely, there is no algorithm deciding, for a given set T consisting of Tuple Generating Dependencies (a.k.a. Datalog program), whether the T -chase on D will terminate for every finite database instance D. Our method applies to Oblivious Chase, Semi-Oblivious Chase and – after a slight modification – also for Standard Chas...