Editing Data type (section)

==Definition==

{{harvtxt|Parnas|Shore|Weiss|1976}} identified five definitions of a "type" that were used—sometimes implicitly—in the literature:
; Syntactic: A type is a purely [[syntax|syntactic]] label associated with a [[variable (computer science)|variable]] when it is declared. Although useful for advanced type systems such as [[substructural type system]]s, such definitions provide no intuitive meaning of the types.
; Representation: A type is defined in terms of a composition of more primitive types—often machine types.
; Representation and behaviour: A type is defined as its representation and a set of [[operator (computer programming)|operator]]s manipulating these representations.
; Value space: A type is a set of possible values which a variable can possess. Such definitions make it possible to speak about ([[disjoint union|disjoint]]) [[union (set theory)|union]]s or [[Cartesian product]]s of types.
; Value space and behaviour: A type is a set of values which a variable can possess and a set of [[function (computer science)|function]]s that one can apply to these values.

The definition in terms of a representation was often done in imperative languages such as [[ALGOL]] and [[Pascal (programming language)|Pascal]], while the definition in terms of a value space and behaviour was used in higher-level languages such as [[Simula]] and [[CLU (programming language)|CLU]]. Types including behavior align more closely with [[object-oriented]] models, whereas a [[structured programming]] model would tend to not include code, and are called [[plain old data structure]]s.