Glenn R. Thompson

Database integration in a distributed heterogeneous database system

This paper describes the approach to database integration in a heterogeneous distributed database environment utilized by the Amoco Distributed Database System (ADDS). We start with the definition of the extended relational data model that is used by ADDS for database integration. We demonstrate various aspects of resolving possible data conflicts occurring in the database integration process. The ADDS query and data definition languages are defined and their expressive power is discussed. We conclude with presentation of a query conversion algorithm to convert a user data request into a set of queries against supported physical databases.

Reliable transaction management in a multidatabase system

A model of a multidatabase system is defined in which each local DBMS uses the two-phase locking protocol Locks are released by a global transaction only after the transaction commits or aborts at each local site. Failures may occur during the processing of transactions. We design a fault tolerant transaction management algorithm and recovery procedures that retain global database consistency. We also show that our algorithms ensure freedom from global deadlocks of any kind.

Transaction management issues in a failure-prone multidatabase system environment

This paper is concerned with the problem of integrating a number of existing off-the-shelf local database systems into a multidatabase system that maintains consistency in the face of concurrency and failures.The major difficulties in designing such systems stem from the requirements that local transactions be allowed to execute outside the multidatabase system control, and that the various local database systems cannot participate in the execution of a global commit protocol. A scheme based on the assumption that the component local database systems use the strict two-phase locking protocol is developed. Two major problems are addressed: How to ensure global transaction atomicity without the provision of a commit protocol, and how to ensure freedom from global deadlocks.

Design issues in distributed multidatabase systems

Many reports have been published on the design strategies employed in the development of multidatabase systems. This paper examines some of these strategies and compares the design of the ADDS system to other efforts in the development of multidatabase systems. There are a number of interesting issues that arise when considering the design of a distributed multidatabase system. These include: (1) the levels of update control for the supported physical databases, (2) the cooperation of the global and local concurrency control schemes, (3) the treatment of concurrency control of a partially replicated distributed multidatabase directory, (4) reduced data transmission with enhanced semijoin algorithms and localized processing of intermediate query results, and (5) the network architecture required to support a distributed multidatabase system.

Are standards the panacea for heterogeneous distributed DBMSs

Applications exist today in a wide variety of industries (for example, the oil industry, automobile manufacturing, and the banking industry) that require the integration of multiple existing distributed databases. Current database management systems (DBMSS) do not satisfy the requirements for these complex applications. Therefore, it is important for the database research community to provide leadership in this rapidly growing area so that future database systems better serve the needs of industry.

Multidatabase performance evaluation

A model of a multidatabase transaction management system is presented, and the performance of two concurrency control algorithms operating in such an environment is analyzed. One algorithm does not impose any restrictions on either the structure of the concurrency control mechanisms used by local database management systems (DBMSs) or the type of multidatabase transactions. The other algorithm assumes that each local DBMS uses the two-phase locking protocol. The performance results presented demonstrate that in both cases the concurrent processing of global transactions provides a better throughput than their serial execution. However, the first algorithm may cause a significant number of global transaction rollbacks for some combinations of local and global transactions. For the second algorithm it is shown that the number of global transaction rollbacks is quite small for reasonable multiprogramming levels and that it performs almost as well as a distributed homogeneous database system.<<ETX>>