POLYGON JOIN DEPENDENCIES, CLOSED CO-RELATIONSHIP CHAINS AND THE CONNECTION TRAP IN RELATIONAL DATA BASES
Date
1987-08-01
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Abstract
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.
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Computer Science