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Relational calculus in a library

  1. Feb 4, 2016 #1
    Let's assume that the Congress library has a database with the
    following pattern (the primary keys are in bold)
    Borrowing(People, Book, DateBorrowing, ExpectedReturnDate,
    EffectiveReturnDate) Lateness(People, Book, DateBorrowing,LatenessFee)
    Who are those that have never return a book late in relational algebra? In relational calculus?

    I think that in relational algebra, they are: $$\Pi_{People}(Borrowing)\div \Pi_{People}(Delayness)$$ But I'm not sure!

    And I definitly don't know how to turn out that in relational calculus...

    $$\{t.People|Delayness(t)\wedge\dots$$

    Have you any hint?
     
  2. jcsd
  3. Feb 4, 2016 #2

    Mark44

    Staff: Mentor

    I'm not sure there's a division operation in relational algebra or relational calculus (I don't know if there's a difference between these two areas).

    In any case, the people who have never returned a book late are those people whose EffectiveReturnDate is on or before their ExpectedReturnDate.
     
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