1.3. The Relational Model
Relational databases use the relational data model popularized by E. F. Codd and C. J. Date. The relational model represents data as entities. An entity is a real-world object, such as a customer or an order. Each entity is represented by a row in a table. Rows are referred to as tuples and consist of a series of attributes (columns). Entities have state, which consists of the values of the attributes (columns). Each column has a single value drawn from a domain of appropriate values.
Most relational databases have the concept of a distinct type, usually a restriction of a simple type such as integer, which comes close to (but does not exactly correspond to) SQL-99's definition of a domain of values. An example of a ...
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