Data model: Difference between revisions

Revision as of 15:09, 9 October 2002

Revision as of 11:35, 27 January 2003

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A '''data model is''' is a model that describes in an abstract way how data is represented in an [[information system]] or a [[database]]. In general it describes the following aspects:

According to [[Fabian Pascal]], a data model is ''a general theory of data defining structural, integrity and manipulation features.''

# ''Structure:'' defines what the structure of the representation is. This should not only specify how data is represented but also how a schema can be specified that defines the structure of the data in a specifi user ___domain.

# ''Integrity:'' provides a language for the definition of rules that restrict which instances of the defined structure are allowed.

# ''Manipulation:'' provides a language in which updates of the data can be expressed.

# ''Querying:'' provides a language in which the data can be queried.

ForAn example, the general theory inis the [[relational model]] is two-valued predicate logic and setin theory;which the structure is that of relations; integritydata is assureddefined byas declaredsubsets constraints, and manipulation is made through relational algebra and calculus.of

[[n-ary relation]]s. It furthermore defines a set of specific constraints (candidate keys, foreign keys, functional dependencies, multi-valued dependencies, join dependencies) and a general language for specifying constraints ([[first-order logic]]), and for manipulations and querying the data the [[relational algebra]], [[tuple calculus]] and [[___domain calculus]] are introduced.

Other examples are the [[Entity-Relationship Model]] and [[ORM]].