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The Computer Journal 1988 31(2):141-146; doi:10.1093/comjnl/31.2.141
© 1988 by British Computer Society
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Polygon Join Dependencies, Closed Co-relationship Chains and the Connection Trap in Relational Databases

J. Bradley *

University of Calgary, The Department of Computer Science, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Co-relationships between relations occur when both attributes supporting the relationship are non-primary keys. A co-relationship can have at least three levels of semantic significance. A special case arises when relations are linked in a closed chain by co-relationships that have existential semantic significance. For binary relations in such a closed chain, it is shown that there is a fundamental theorem that prohibits extraction of reliable information from a complete join of the relations, unless the join contains a polygonal join dependency of order equal to the number of relations in the chain. Users who ignore this restriction fall into a sophisticated connection trap.

Received January 1987. revised August 1987.

* University of Calgary, The Department of Computer Science, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4


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