A data model is a formal description of entities and their relationships, and of operations allowed on the entities. A data model is independent of a specific DBMS implementation. An instance of a data model or database schema is a data definition based on the data types and the data manipulation commands provided by the DBMS.
Data modelling is the process of describing the world of interest in the terms of a data model.
The following data models can be discerned:
The development of the data models can be characterised as a) continued abstraction from physical storage, and b) increase in expressive power.