July 2010
Intermediate to advanced
976 pages
30h 19m
English
Content preview from Information Modeling and Relational Databases, 2nd Edition
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7.6. Summary
CSDP step 7 adds other constraints and performs final checks. An occurrence frequency constraint indicates that an entry in a column (or column combination) must occur there exactly n times in), at most n times (≤ n), at least n times (≥ n), or at least n and at most m times (n .. m). A simple occurrence frequency appears next to the role. A compound occurrence frequency appears next to a line connecting the relevant roles.
A ring constraint can apply only to a pair of roles played by the same (or a compatible) object type. The role pair may form a binary predicate or be embedded in a longer predicate. Let R be the relation type comprising the role pair. R is reflexive (over its populations) iff for all x playing either role,
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