July 2008
Intermediate to advanced
230 pages
4h 33m
English
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Chapter 24. W
well-formed formula In logic, a formal expression denoting a predicate.
WFF A well-formed formula. The abbreviation is variously pronounced "weff" or "wiff" or "woof." See closed WFF; open WFF.
what if A read-only relational operator that returns the relation that would result if certain changes were made to a specified relation (ignoring the fact that such changes couldn't in fact be made, because a relation is a value).
Example: Consider the following expression:
UPDATE S WHERE CITY = 'Paris' :
{ STATUS := 2 * STATUS , CITY := 'Nice' }Observe that, even though it uses the keyword UPDATE, this expression is indeed an expression and not a statement (it has no terminating semicolon); in particular, it has no effect on relvar S. What it ...
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