# relational algebra

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## relational algebra

(database, theory)
A family of algebra with a well-founded semantics used for modelling the data stored in relational databases, and defining queries on it. The main operations of the relational algebra are the set operations (such as union, intersection, and cartesian product), selection (keeping only some lines of a table) and the projection (keeping only some columns).

The relational data model describes how the data is structured.

Codd's reduction algorithm can convert from relational calculus to relational algebra.

## relational algebra

(1) The branch of mathematics that deals with relations; for example, AND, OR, NOT, IS and CONTAINS.

(2) In a relational database, a collection of rules for dealing with tables; for example, JOIN, UNION and INTERSECT.
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References in periodicals archive ?
In the first step, the relational algebra is extended with new operators that execute the most expensive processes of association and classification tasks.
Pirotte, "A precise definition of basic relational notions and of the relational algebra," ACM SIGMOD Record, vol.13, no.1, pp.30-45, 1982.
* Rules for combining operands and operators to relational algebra expression
In this section we consider a more specific framework of update methods implemented in the relational algebra, inspired by the algebraic model of object-oriented database access introduced by Hull and Su [1989].
Since the relational algebra and calculus are equivalent to pure first-order logic, they have [AC.sup.0] data complexity, cf.
So any expression in our probabilistic relational algebra yields a probabilistic relation.
Compaction is the TP analog of duplicate elimination in the relational algebra.
The estimate operator is classified by the relational algebra operator (select, project, join), the property to be estimated (cardinality, distribution of values, and other parameters), and the underlying method (parametric, nonparametric, and ad-hoc).
This mapping assumes a mapping of SQL-92 to relational algebra and defines temporal statements in terms of their mapping to well-defined temporal and conventional relational algebra expressions.
Extending Relational Algebra and Relational Calculus with
OQL queries in our framework are translated into a calculus format that serves as an intermediate form, and then are translated into a version of the nested relational algebra. We use both a calculus and an algebra as intermediate forms because the calculus closely resembles current OODB languages and is easy to put into canonical form, while the algebra is lower-level and can be directly translated into the execution algorithms supported by database systems.
MATCH is a new operator for relational algebra which provides a natural and nonprocedural means to express retrievals based on very complex patterns which are themselves stored as data.

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