Database Management System (DBMS) Basic Concepts

Entity - Relationship Model

The Entity - Relationship Model (E-R Model) is a high-level conceptual data model developed by Chen in 1976 to facilitate database design. Conceptual Modeling is an important phase in designing a successful database. A conceptual data model is a set of concepts that describe the structure of a database and associated retrieval and updation transactions on the database. A high level model is chosen so that all the technical aspects are also covered.

The E-R data model grew out of the exercise of using commercially available DBMS's to model the database. The E-R model is the generalization of the earlier available commercial models like the Hierarchical and the Network Model. It also allows the representation of the various constraints as well as their relationships.

So to sum up, the Entity-Relationship (E-R) Model is based on a view of a real world that consists of set of objects called entities and relationships among entity sets which are basically a group of similar objects. The relationships between entity sets is represented by a named E-R relationship and is of 1:1, 1: N or M: N type which tells the mapping from one entity set to another.

The E-R model is shown diagrammatically using Entity-Relationship (E-R) diagrams which represent the elements of the conceptual model that show the meanings and the relationships between those elements independent of any particular DBMS and implementation details.

Features of the E-R Model:

1. The E-R diagram used for representing E-R Model can be easily converted into Relations (tables) in Relational Model.

2. The E-R Model is used for the purpose of good database design by the database developer so to use that data model in various DBMS.

3. It is helpful as a problem decomposition tool as it shows the entities and the relationship between those entities.

4. It is inherently an iterative process. On later modifications, the entities can be inserted into this model.

5. It is very simple and easy to understand by various types of users and designers because specific standards are used for their representation.