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Publications (7)0 Total impact

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    J.M. Morrissey · W.K. Osborn · Y. Liang
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    ABSTRACT: The optimization of general queries in a distributed database management system is an important research issue. The problem is to select the best sequence of database operations that will process the query efficiently and minimize costs. Approaches include algorithms which are join-based, semijoin-based, or a combination of both. The algorithm presented which is based on reduction filters, can process general queries consisting of an arbitrary number of relations and join attributes. Each query is represented by a graph and an adjacency list. Each relation is usually only processed once, to minimize data transfers. However, if a filter changes during use then certain relations must be processed again; a queue is used to record this information. The algorithm consists of two phases: during phase one the adjacency list is used to determine the order in which the filters are constructed and used
    Electrical and Computer Engineering, 2000 Canadian Conference on; 02/2000
  • J.M. Morrissey · O. Ogunbadejo
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    ABSTRACT: Tseng and Chen (1992) presented a new relational operator called a hash-semijoin. They proposed a method which will transform a sequence of semijoins, produced by any existing semijoin-based algorithm, into a more cost effective sequence by replacing some of the semijoins by hash-semijoins. The hash-semijoin can be very effective but some of the benefits may be negated by the occurrence of collisions in the reduction filter. Such collisions mean that the hash-semijoin cannot achieve the same amount of reduction as a semijoin can. However, under certain circumstances, the benefits may greatly outweigh the costs and thus collisions are not a serious problem. But their approach has not been experimentally evaluated. In this paper we explore their hypothesis that traditional algorithms, which use semijoins, can always be improved by replacing some or all of the semijoins by hash-semijoins. Four different algorithms are investigated. Each aims to minimize the amount of data transmitted around the network during distributed query processing
    Electrical and Computer Engineering, 1999 IEEE Canadian Conference on; 02/1999
  • Source
    J.M. Morrissey · W.K. Osborn
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    ABSTRACT: The optimization of general queries in a distributed database management system is an important research topic. The problem is to select the best sequence of database operations that will process the query and minimize costs. Our algorithm, which is based on reduction filters, can process general queries consisting of an arbitrary number of relations and join attributes. Each query is represented by a graph and an adjacency list. Each relation is usually only processed once-to minimize data transfers. However, if a filter changes during use then certain relations must be processed again-a queue is used to record this information. This work has one serious limitation-we used a “perfect“ hash function which means that collisions are not possible. Experiments showed that our algorithm could reduce data transfers very substantially. However, in a database collisions in the reduction filter are a reality and a problem. Such collisions mean that the hash-semijoin cannot achieve the same amount of reduction as a traditional semijoin would. We investigate the effect that collisions have on the performance of our algorithm
    Electrical and Computer Engineering, 1999 IEEE Canadian Conference on; 02/1999
  • Source
    J.M. Morrissey · W.K. Osborn
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    ABSTRACT: The optimization of general queries in a distributed database management system is an important research topic. The difficulty is to select the database operations which will process the query and minimize costs. Traditional solutions include the use of heuristic strategies based on semijoin or join operations. We present an approach for general queries which uses reduction filters, which are based on Bloom filters, to minimize data transfers and reduce local processing costs. We discuss related work and present our algorithm-illustrating it with a simple example. We end with a brief discussion of current and future work
    Electrical and Computer Engineering, 1998. IEEE Canadian Conference on; 06/1998
  • S. Bandyopadhyay · J. Morrissey · A. Sengupta
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    ABSTRACT: In the last ten years, optical communication has become a viable technology and is rapidly replacing computer communication based on copper wires. The speed of optical communication is much higher than the speed of electronic devices and we now need to re-examine the cost criteria for data communication in distributed computing. We have shown that the basic assumptions in query optimization for distributed databases are not valid in all-optical networks. We have proposed a new strategy for query optimization appropriate for such networks
    Electrical and Computer Engineering, 1996. Canadian Conference on; 06/1996
  • J.M. Morrissey
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    ABSTRACT: It has long been recognized that query optimization in distributed database systems is an important research issue. The challenge is to determine a sequence of operations which will process the query while minimizing the chosen cost function. Finding the optimal optimization for a general query is an NP-hard problem so, in general, heuristics are employed to find a cost-effective and efficient processing method. We present a novel approach to the problem, which uses reduction filters, with the objective of minimizing the total volume of data transferred in the network. We assume a distributed relational database management system and select-project-join queries. This means that we have a number of relations, each located at a different site in the network, which must be joined and the result made available at some distinct query site. Our technique is to reduce the relations, before shipment to the query site, using reduction filters and thereby significantly reduce the total communication cost
    Electrical and Computer Engineering, 1996. Canadian Conference on; 06/1996
  • J.M. Morrissey · S. Bandyopadhyay
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    ABSTRACT: The premise of this paper is that query optimization in distributed databases can be improved by taking into account certain parameters such as the network architecture and communication delays. Current heuristics make simplistic assumptions, disregarding the actual characteristics of the network. Here, we assume that the network and distributed database managers will communicate and propose a heuristic which utilizes available delay information to minimize the total response time. Initial experiments indicate that our heuristic performs well in comparison to other distributed query optimization algorithms
    Electrical and Computer Engineering, 1995. Canadian Conference on; 10/1995