ics321-20091006-relcalc

ics321-20091006-relcalc - S.b • R.a<>.= constant or...

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ICS 321 Fall 2009 Relational Calculus Asst. Prof. Lipyeow Lim University of Hawaii at Manoa 10/06/2009 1 Lipyeow Lim -- University of Hawaii at Manoa
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Relational Calculus (RC) RC is an alternative to RA RC is non-procedural, or declarative: describe what the results of a query should be without specifying how to get the results Two variants: Tuple Relational Calculus Domain Relational Calculus (not covered in ICS321) 10/06/2009 Lipyeow Lim -- University of Hawaii at Manoa 2
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Tuple Relational Calculus (TRC) Uses tuple variables : a variable that takes on tuples of a particular relation schema as values. A TRC query is specified using set-theoretic first order logic expressions of the form { T | p(T) } T is a tuple variable and is the only free variable in p p(T) is a formula that describes T Any atomic formula R Rel R.a {<>.=,
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Unformatted text preview: , , } S.b • R.a {<>.=, , , } constant, or constant {<>.=, , , } R.a – p, p q, p q, p q – R( p(R) ), where R is a tuple variable – R( p(R) ), where R is a tuple variable 10/06/2009 Lipyeow Lim -- University of Hawaii at Manoa 3 Q11: Find all sailors with rating above 7 • The TRC expression for this query is { S | S Sailors S.rating > 7 } • Reads: the set of S tuples, such that S is a member of the Sailors relation instance AND S’s rating is greater than 7. 10/06/2009 Lipyeow Lim -- University of Hawaii at Manoa 4 Q12: Find the names and ages of sailors with a rating above 7 • The TRC expression for this query is { P | S Sailors (S.rating > 7 P.name=S.name P.age=S.age ) } 10/06/2009 Lipyeow Lim -- University of Hawaii at Manoa 5...
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This note was uploaded on 11/15/2010 for the course ICS 321 taught by Professor Lim during the Fall '09 term at University of Hawaii, Manoa.

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ics321-20091006-relcalc - S.b • R.a<>.= constant or...

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