الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
In the recent years, steady improvements in computer hardware and network technology have led to dramatic increase in the information technology. Generally, it can be said that information retrieving and data collecting are the most important requirements in the information technology. The most recent researches in this field are concentrating on increasing the network utilization by increasing the data transfer rate (developing high data transfer rate shared channels, and enhancing the network protocols to solve the bottle neck and traffic problems), and optimizing the volume of data transmission through the network. The main objective of this thesis is to introduce new algorithms of data retrieving that reduce the volume of data transmission on networks during distributed query execution. The proposed algorithms are focusing on distributed query optimization problem, especially on optimization of the join operation because of its complexity and importance besides that it incurs transmission of unwanted data on the network that is not included in the final results. The thesis proposes new temporary relations called join views. Join views are proved to reduce semijoin costs during the distributed query execution. It also proposes two new heuristic semijoin join view based algorithms, HSJV and HPSJV algorithms. Both algorithms are proved to reduce the volume of data transmission with high efficiencies compared to a common method. Information retrieval in computer networks can be supported much more efficiently if an agent representing a query can move to the place where the data are actually stored. Consequently, this thesis also proposes a new dynamic distributed query execution algorithm. The algorithm is based on mobile agents in executing the join queries. Mobile agents are autonomous agents capable of migration from site to site. The algorithm is proved to dynamically give high reduction in the volume of data transmitted on the network compared to the enhanced direct method. The potential of updating join views is being treated by mobile agents where a mobile agents based update algorithm is proposed as well.