<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> A relational database is a digital database based on the relational model of data, as proposed by E.F. Codd in 1970 . A software system used to maintain relational databases is a relational database management system (RDBMS). Virtually all relational database systems use SQL (Structured Query Language) for querying and maintaining the database . </P> <P> This model organizes data into one or more tables (or "relations") of columns and rows, with a unique key identifying each row . Rows are also called records or tuples . Columns are also called attributes . Generally, each table / relation represents one "entity type" (such as customer or product). The rows represent instances of that type of entity (such as "Lee" or "chair") and the columns representing values attributed to that instance (such as address or price). </P> <P> Each row in a table has its own unique key . Rows in a table can be linked to rows in other tables by adding a column for the unique key of the linked row (such columns are known as foreign keys). Codd showed that data relationships of arbitrary complexity can be represented by a simple set of concepts . </P>

In a relational database a record is also called a(n)