Editing Data model (section)

=== Data model theory ===
The term data model can have two meanings:<ref name="Beynon-Davies P. 2004">Beynon-Davies P. (2004). Database Systems 3rd Edition. Palgrave, Basingstoke, UK. {{ISBN|1-4039-1601-2}}</ref>
# A data model ''theory'', i.e. a formal description of how data may be structured and accessed.
# A data model ''instance'', i.e. applying a data model ''theory'' to create a practical data model ''instance'' for some particular application.

A data model theory has three main components:<ref name="Beynon-Davies P. 2004"/>
* The structural part: a collection of data structures which are used to create databases representing the entities or objects modeled by the database.
* The integrity part: a collection of rules governing the constraints placed on these data structures to ensure structural integrity.
* The manipulation part: a collection of operators which can be applied to the data structures, to update and query the data contained in the database.

For example, in the [[relational model]], the structural part is based on a modified concept of the [[Relation (mathematics)|mathematical relation]]; the integrity part is expressed in [[first-order logic]] and the manipulation part is expressed using the [[relational algebra]], [[tuple calculus]] and [[domain calculus]].

A data model instance is created by applying a data model theory. This is typically done to solve some business enterprise requirement. Business requirements are normally captured by a semantic [[logical data model]]. This is transformed into a physical data model instance from which is generated a physical database. For example, a data modeler may use a data modeling tool to create an [[entity–relationship model]] of the corporate data repository of some business enterprise. This model is transformed into a [[relational model]], which in turn generates a [[relational database]].