An approach to concurrency control is presented; it is based on the decomposition of both the database and the individual transactions. This approach is a generalization of serializability theory in that the set of permissible transaction schedules contains all the serializable schedules. In addition to providing a higher degree of concurrency than that provided by serializability theory, this approach retains three important properties associated with serializability: the consistency of the database is preserved, the individual transactions are executed correctly, and the concurrency control approach is modular. The authors formalize the last concept. The associated failure recovery procedure is presented, as is the concept of failure safety (i.e. failure tolerance). >