Relational Calculus

See: Relation Function, Tuple, Relational Database, Lambda Calculus, Predicate Calculus.

---

---

References

• (Wikipedia, 2009) ⇒ http://en.wikipedia.org/wiki/Relational_calculus
  • Relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries. This in contrast to the relational algebra which is also part of the relational model but provides a more procedural way for specifying queries.
  • The relational algebra might suggest these steps to retrieve the phone numbers and names of book stores that supply Some Sample Book:
    • 1. Join books and book stores over the BookstoreID.
    • 2. Restrict the result of that join to tuples for the book Some Sample Book.
    • 3. Project the result of that restriction over StoreName and StorePhone.
  • The relational calculus would formulate a descriptive, declarative way:
    • Get StoreName and StorePhone for supplies such that there exists a title BK with the same BookstoreID value and with a BookTitle value of Some Sample Book.
    • The relational algebra and the relational calculus are essentially logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa. This result is known as Codd's theorem.

---