Relational calculus consists of two calculi, the
tuple relational calculusThe tuple calculus is a calculus that was introduced by Edgar F. Codd as part of the relational model in order to give a declarative database query language for this data model...
and the
domain relational calculusIn computer science, domain relational calculus is a calculus that was introduced by Michel Lacroix and Alain Pirotte as a declarative database query language for the relational data model.In DRC, queries have the form:...
, that are part of the
relational modelThe relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by E.F. Codd.- Overview :...
for databases and provide a declarative way to specify database queries. This in contrast to the
relational algebraRelational algebra, an offshoot of first-order logic , deals with a set of finitary relations which is closed under certain operators. These operators operate on one or more relations to yield a relation...
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 book stores 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 essentially logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa.
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Relational calculus consists of two calculi, the
tuple relational calculusThe tuple calculus is a calculus that was introduced by Edgar F. Codd as part of the relational model in order to give a declarative database query language for this data model...
and the
domain relational calculusIn computer science, domain relational calculus is a calculus that was introduced by Michel Lacroix and Alain Pirotte as a declarative database query language for the relational data model.In DRC, queries have the form:...
, that are part of the
relational modelThe relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by E.F. Codd.- Overview :...
for databases and provide a declarative way to specify database queries. This in contrast to the
relational algebraRelational algebra, an offshoot of first-order logic , deals with a set of finitary relations which is closed under certain operators. These operators operate on one or more relations to yield a relation...
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 book stores 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 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 theoremCodd's theorem states that relational algebra and the domain-independent relational calculus queries, two well-known foundational query languages for the relational model, are precisely equivalent in expressive power. That is, a database query can be formulated in one language if and only if it can...
.
See also
- The Third Manifesto
The Third Manifesto is Christopher J. Date's and Hugh Darwen's proposal for future database management systems, a response to two earlier Manifestos with the same purpose. The theme of the manifestos is how to avoid the 'object-relational impedance mismatch' between object-oriented programming...
- Tutorial D
- D (data language specification)
D is a set of requirements proposed by Christopher J. Date and Hugh Darwen in their book The Third Manifesto for what they believe a relational database query language ought to be like; D is not a language itself.- Overview :...
- D4 (programming language)
D4 is a computer language used in Dataphor, a relational database management system.-Syntax:Alphora, the creators of D4, have given it a Pascal like syntax...
(an implementation of D)
- Aldat Relational Algebra