FLEXIBLE CONSISTENCY MODES FOR ACTIVE DATABASES APPLICATIONS

The concept of transaction is a basic one in database theory. Yet, in some cases the atomicity of a transaction may be relaxed. This happens either to avoid the damage inflicted by the fact that many data eleme nts are locked in long transactions, or to support different view-poin ts of the database that may relax atomicity constraints. This paper de fines the concept of transaction, in the environment of PARDES-an inte lligent active database and outlines a model in which different modes of consistency co-exist as local decisions. These modes are defined an d analyzed. Among the basic modes are: fully consistent (consistent at all times), quasi consistent (eventually consistent) and loosely cons istent (failures in derivations are not compensated). This is an exten sion to the active database definition language that enables the suppo rt of implementation considerations using high-level abstractions.