Autonomy Requirements in Heterogeneous Distributed Database Systems

In the context of multidatabase systems and heterogeneous distributed database systems , it has been observed that autonomy of the component databases has to be violated in order to maintain traditional database and transaction properties. However, very little work exists that systematically analyzes (a) the semantics of autonomy and (b) the implications of autonomy vis a vis correctness speciications and database protocols. Hence, this paper is aimed at characterizing the diierent types of autonomy by focusing on transaction management and showing the relationships between autonomy requirements and database protocols. As a case-study, we investigate the autonomy implications of the two-phase commit protocol and its multidatabase variants. Our analysis shows that these protocols involve tradeoos between the autonomy of the transactions, with respect to accessing the data objects, and the autonomy of the transaction management system, with respect to responding to the transaction management primitives. As a result, this paper brings out the practical considerations involved in selecting between alternative protocols.