Database Model

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Database Model
A database model or database schema is the structure or format of a database, described in a formal language supported by the database management system. Schemas are generally stored in a data dictionary.
Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure.

Overview
A database model is a theory or specification describing how a database is structured and used. Several such models have been suggested.

Common models include:

Hierarchical model
Network model
Relational model
Entity-relationship
Object-relational model
Object model
A data model is not just a way of structuring data: it also defines a set of operations that can be performed on the data. The relational model, for example, defines operations such as select, project, and join. Although these operations may not be explicit in a particular query language, they provide the foundation on which a query language is built.