Abstract
Many classical database problems such as semantic optimization, minimization, rewriting using views, equivalent query reformulation in data publishing and integration, are particular instances of query reformulation under constraints. while the general reformulation problem is undecidable, the least restrictive known conditions which are sufficient to guarantee decidability hold in numerous practical scenarios. C&B is a sound and complete algorithm, which provide a uniform solution to the above database problems. The C&B method is viable in practice with careful engineering of the chase and backchase phases.