On Determining Tree Query Membership Of A Distributed Query
Clement T. Yu, Meral Özsoyoğlu · INFOR Information Systems and Operational Research · 1984
In processing distributed relational database queries, the cost of communication between sites is the dominant cost factor. It is generally agreed that the amount of data transferred determines this communication cost to a large extent. Thus it is desirable to minimize the amount of transmitted data.Semi-join is a relational database operator which can be utilized to reduce the amount of data transmission in processing distributed queries. A class of queries, called tree queries, can always be answered using semi-joins. In this paper an algorithm is presented which decides whether or not a query involvingjoin clauses with relational operators {} is a tree query. For any tree query the algorithm also produces a tree query graph, so that the sequences of semi-joins to answer the query can immediately be determined.