Domain relational calculus - AbsoluteAstronomy.com

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, domain relational calculus (DRC) is a calculus that was introduced by Michel Lacroix and Alain Pirotte as a declarative

Declarative programming

In computer science, declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow. Many languages applying this style attempt to minimize or eliminate side effects by describing what the program should accomplish, rather than...

database query language

Query language

Query languages are computer languages used to make queries into databases and information systems.Broadly, query languages can be classified according to whether they are database query languages or information retrieval query languages...

for the relational data model

Relational model

The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...

.

In DRC, queries have the form:

where each X_i is either a domain variable or constant, and

denotes a DRC formula. The result of the query is the set of tuples X_i to X_n which makes the DRC formula true.

This language uses the same operators as tuple calculus,
the logical connectives ∧ (and), ∨ (or) and ¬ (not). The existential quantifier

Existential quantification

In predicate logic, an existential quantification is the predication of a property or relation to at least one member of the domain. It is denoted by the logical operator symbol ∃ , which is called the existential quantifier...

(∃) and the universal quantifier

Universal quantification

In predicate logic, universal quantification formalizes the notion that something is true for everything, or every relevant thing....

(∀) can be used to bind the variables.

Its computational expressiveness is equivalent to that of Relational algebra

Relational algebra

Relational algebra, an offshoot of first-order logic , deals with a set of finitary relations that is closed under certain operators. These operators operate on one or more relations to yield a relation...

Examples

Let (A, B, C) mean (Rank, Name, ID)

and (D, E, F) to mean (Name, DeptName, ID)

Find all captains of the starship USS Enterprise

USS Enterprise (NCC-1701)

The USS Enterprise, NCC-1701, is a fictional starship in the Star Trek media franchise. The original Star Trek series depicts her crew's mission "to explore strange new worlds; to seek out new life and new civilizations; to boldly go where no man has gone before" under the command of Captain James...

In this example, A, B, C denotes both the result set and a set in the table Enterprise.

Find Names of Enterprise crewmembers who are in Stellar Cartography:

In this example, we're only looking for the name, and that's B. F = C is a requirement, because we need to find Enterprise crew members AND they are in the Stellar Cartography Department.

An alternate representation of the previous example would be:

In this example, the value of the requested F domain is directly placed in the formula and the C domain variable is re-used in the query for the existence of a department, since it already holds a crew member's id.

Examples

See also