Execution plans generated by traditional optimizers for large scale distributed queries can be sub-optimal because: the estimations are inaccurate, the data are unavailable and the execution environment is unstable. T...
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(纸本)0769524346
Execution plans generated by traditional optimizers for large scale distributed queries can be sub-optimal because: the estimations are inaccurate, the data are unavailable and the execution environment is unstable. To deal with the sub-optimality, we propose to execute each relational operator of an execution plan by a mobile agent. A mobile agent can change its execution site in order to correct the sub-optimality. In this paper, we address the problem of choosing an execution site for a mobile agent among execution sites of the considered system. For this, we propose to integrate a cost model into the mobile agents. We define also the various interactions that might occur between a mobile agent and its execution site. The performance evaluation shows that the cost model embedded in the agent allows to choose the most appropriate execution site.
The problem of mining association rules and its relative parallel mining algorithms is presented. The problems that existing algorithms can cause low efficiency and information lost in heterogeneousdistributed databa...
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The problem of mining association rules and its relative parallel mining algorithms is presented. The problems that existing algorithms can cause low efficiency and information lost in heterogeneous distributed databases is pointed out. An asynchronous parallel algorithm based on our HDDMiner system for mining association rules in heterogeneous distributed databases is given after a basic theory is proved. Some problems involved are discussed in detail as well. At the end of this paper, several key issues in the research of parallel algorithms in heterogeneous distributed databases are introduced.
The problem of retrieving information from a collection of heterogeneous distributed databases has attracted a number of solutions. However, the task of integrating established database systems is complicated not only...
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The problem of retrieving information from a collection of heterogeneous distributed databases has attracted a number of solutions. However, the task of integrating established database systems is complicated not only by the differences between the database systems themselves, but also by the differences in structure and semantics of the information contained within them. The problem is exacerbated when one needs to provide access to such a system for naive end-users. This paper is concerned with a Knowledge-Based Systems approach to solving this problem for clearly bounded situations, in which both the domain and the types of query are constrained. At the user interface, dialogue is conducted in terms of concepts with which the user is familiar, and these are then mapped into appropriate database queries. To achieve this a model for query decomposition and answer construction has been used. This model is based around the development of an Intensional Structure containing information necessary for the recapture of semantic information lost in the query decomposition process and required in the answer construction process. The model has been successfully implemented in combination with an embedded KBS, within a five-layer representation model.
We present an extension to the object model of OMT to cope with bottom-up database design. By investigation, it was discovered that OMT as it stands is inadequate to capture some real world semantic and structural inf...
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We present an extension to the object model of OMT to cope with bottom-up database design. By investigation, it was discovered that OMT as it stands is inadequate to capture some real world semantic and structural information needed to perform schema integration for pre-existing databases in a heterogeneousdistributed database environment. Therefore the proposed extension, called Integrated OMT (IOMT), was formally defined and an appropriate extended graphical notation was produced as a part of our work. This extended form was implemented and applied effectively using a tool which we call the schema meta-integration/visualisation system (SMIS/SMVS).
A destination information system (DIS) is defined as an interorganizational system (IOS) that provides travelers and travel counselors with easy access to comprehensive, timely and accurate information on a destinatio...
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A destination information system (DIS) is defined as an interorganizational system (IOS) that provides travelers and travel counselors with easy access to comprehensive, timely and accurate information on a destination's facilities, and the option of making reservations. Its development requires extensive cooperation by competing tourism product suppliers and destination promoters in both the public and private sectors. This paper identifies challenges encountered in the design of a DIS such as: (1) comprehensive information content from multiple data sources, (2) multimedia data management, (3) interfacing with global electronic markets, and (4) resolving problems arising from different data formats and standards. Technical design options are examined to address these design challenges. A proposed system architecture, called VIDIS, integrating viable design options is then presented. The VIDIS architecture exploits current technological advances in heterogeneous distributed databases, intelligent multim edia communication, and global electronic commerce. Implementation strategies of a DIS that adapt to organizational changes and rapid technological advances are suggested. Finally, design tasks and related organizational issues are discussed.
This paper describes the design and implementation of a high-level query language called Generalized Query-By-Rule (GQBR) which supports retrieval, insertion, deletion and update operations. This language, based on th...
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This paper describes the design and implementation of a high-level query language called Generalized Query-By-Rule (GQBR) which supports retrieval, insertion, deletion and update operations. This language, based on the formalism of database logic, enables the users to access each database in a distributedheterogeneous environment, without having to learn all the different data manipulation languages. The compiler has been implemented on a DEC 1090 system in Pascal.
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