FORMAL ASPECTS OF CONCURRENCY-CONTROL IN LONG-DURATION TRANSACTION SYSTEMS USING THE NT PV MODEL/

In the typical database system, an execution is correct if it is equiv alent to some serial execution. This criterion, called serializability , is unacceptable for new database applications which require long-dur ation transactions. We present a new transaction model which allows co rrectness criteria more suitable for these applications. This model co mbines three enhancements to the standard model: nested transactions, explicit predicates, and multiple versions. These features yield the n ame of the new model, nested transactions with predicates and versions , or NT/PV. The modular nature of the NT/PV model allows a straightfor ward representation of simple systems. It also provides a formal frame work for describing complex interactions. The most complex interaction s the model allows can be captured by a protocol which exploits all of the semantics available to the NT/PV model. An example of these inter actions is shown in a CASE application. The example shows how a system based on the NT/PV model is superior to both standard database techni ques and unrestricted systems in both correctness and performance.