There are three levels of data modeling:
(Quote: Alf Alexander Pedersen, databasedesign-resource.com)
The Conceptual Database Model, which is transformed into a
Logical Database Model, which in turn is used to generate the
Physical Database Model.
The Conceptual Model can, for simplicity, be seen as consisting of an Entity-Relationship Model with its Entities, Attributes and Conventions governing those Entities and Attributes.
Informal Predicates, or Conventional rules are spelled out in natural language and transformed into Formal Predicates, which in turn are defined as Constraints in the Logical Database Model.
From the finished Logical Database Model, one can generate all the necessary scripts (CREATE TABLE, INDEX, etc.) that will ultimately implement the Physical Database Model on the system’s hard disk (s).
The three levels of data modeling are compared by their different features:
The Conceptual Data Model serves to understand at high level what the different Entities are and how they relate to one another.
The Logical Data Model serves to understand the details of the data without worrying about how they will actually be implemented.
Finally the Physical Data Model serves to know exactly how to implement the Data Model in the Database of choice. In a Data Warehousing Project, sometimes the Conceptual Data Model and the Logical Data Model are considered as a single deliverable.