Data Model: When we start modeling our data in database systemthe mainly fall into the following category-

High Level/Conceptual Level: Close to the way we actually use those data. Eg. ER Model

Low Level/Physical Level: The way data actually stored in the computer.

Implementation Data Model: It lies somewhere between the ‘High Level’ and ‘Low Level’. The concept can be understood by both, the end user and the programmer. For example: Relational model, Network Model and Hierarchical model.