Relational algebra no relation data model
Data model theory
The term data model can have two meanings:
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:
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 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.
no relation