In relational databases, relvar is a term introduced by C. J. Date and

Hugh Darwen Hugh Darwen is a computer scientist who was an employee of IBM United Kingdom from 1967. to 2004, and has been involved in the development of the relational model. Work From 1978 to 1982 he was a chief architect on Business System 12, a da ...

as an

abbreviation An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters or words taken from the full version of the word or phrase; for example, the word ''abbrevia ...

for relation variable in their 1995 paper ''The Third Manifesto'', to avoid the confusion sometimes arising from the use of the term relation, by the inventor of the

relational model The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tu ...

E. F. Codd Edgar Frank "Ted" Codd (19 August 1923 – 18 April 2003) was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases and relational databa ...

, for a variable to which a relation is assigned as well as for the relation itself. The term is used in Date's well-known database textbook ''An Introduction to Database Systems'' and in various other books authored or coauthored by him. Some database textbooks use the term relation for both the variable and the data it contains. Similarly, texts on SQL tend to use the term ''table'' for both purposes, though the qualified term ''base table'' is used in the standard for the variable. A closely related term often used in academic texts is

relation schema In database theory, a relation, as originally defined by E. F. Codd, is a set of tuples (d1, d2, ..., dn), where each element dj is a member of Dj, a data domain. Codd's original definition notwithstanding, and contrary to the usua ...

, this being a set of attributes paired with a set of constraints, together defining a set of relations for the purpose of some discussion (typically,

database normalization Database normalization or database normalisation (see spelling differences) is the process of structuring a relational database in accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity ...

). Constraints that mention just one relvar are termed ''relvar constraints'', so

can be regarded as a single term encompassing a relvar and its relvar constraints.

References

* C.J. Date. ''An Introduction to Database Systems'', 8th Ed. (Addison-Wesley, 2004, ), pp. 65–6. * C.J. Date and

. ''Databases, Types, and The Relational Model: The Third Manifesto'' (Addison-Wesley, 2007, ), p.85 Relational model Data modeling Databases Variable (computer science) {{database-stub