Everything about Relational Calculus totally explained
Relational calculus consist 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:
- Join books and titles over the BookstoreID.
- Restrict the result of that join to tuples for the book Some Sample Book.
- 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 logically equivalent: for any algebraic expression, there's an equivalent expression in the calculus, and vice versa.
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