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<p>The problem of optimizing joins between two fragmented relations on a broadcast local network is analyzed. Data redundancy is considered. Semantic information associated with fragments are used to eliminate necessary processing. More than one physical copies of a fragment is allowed to be used in a strategy to achieve more parallelism. Join-analysis graphs are introduced to represent joins on two fragmented relations. The problem of optimizing a join is mapped into an equivalent problem of finding a minimum-weight vertex cover for the corresponding join-analysis graph. This problem is proved to be NP-hard. A four-phase approach for processing joins is proposed.</p>
NP hardness; fragmented database systems; broadcast local network; relations; redundancy; parallelism; minimum-weight vertex cover; join-analysis graph; concurrency control; distributed databases; local area networks; relational databases.

J. Chen and V. Li, "Optimizing Joins in Fragmented Database Systems on a Broadcast Local Network," in IEEE Transactions on Software Engineering, vol. 15, no. , pp. 26-38, 1989.
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