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/Internal Level : The internal level is also named as physical level. The internal level express how data is stored in the files, indices .etc. on the storage devices i.e. secondary storage.

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.