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<p>The application of a combination of join and semi-join operations to minimize the amount of data transmission required for distributed query processing is discussed. Specifically, two important concepts that occur with the use of join operations as reducers in query processing, namely, gainful semi-joins and pure joint attributes, are used. Some semi-joint, though not profitable themselves, may benefit the execution of subsequent join operations as reducers. Such a semi-join is termed a gainful semi-join. In addition, join attributes that are not part of the output attributes are referred to as pure join attributes. They exploit the usefulness of gainful semi-joins and use the removability of pure join attributes to reduce the amount of data transmission required for query processing. Heuristic searches are developed to determine a sequence of join and semi-join reducers for query processing. Results indicate the importance of the approach to combining joins and semi-joins for distributed query processing.</p>
join operations; semijoin operations; heuristic searches; distributed query processing; data transmission; reducers; query processing; gainful semi-joins; joint attributes; distributed databases; query processing

M. Chen and P. Yu, "Combining Joint and Semi-Join Operations for Distributed Query Processing," in IEEE Transactions on Knowledge & Data Engineering, vol. 5, no. , pp. 534-542, 1993.
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