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The paper suggests the heuristic approach for selecting the optimal evaluation plan and Semi-join approach for reducing the communication cost. Calculating the cost of each evaluation plan of a query takes lots of computational efforts as well as time. Initially the heuristic approach is used to find best evaluation plan among various plans of a single query. By considering only joins, queries are divided into two: tree and cyclic. Semi-join is a useful tool to reduce the cost of joins. The communication cost in distributed database is mainly depending upon the amount of data transferred from one site to another site.
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