A THEORETICAL FORMULATION FOR DEGREES OF ISOLATION IN DATABASES

Although isolation is one of the desirable properties, most commercial database management systems do not provide complete isolation to tran sactions. They offer different degrees - 0, 1, 2, or 3 - of isolation, to transactions. By providing lower degrees of isolation, response ti me of a database system can be improved, although at the expense of co nsistency. Originally different degrees of isolation were defined in t erms of lock-based protocols. This paper formulates these different de grees of isolation in terms of histories, as in the case of the usual serialization theory and proposes timestamp-based protocols for differ ent degrees of isolation.