Introduction to ER Model | Database Management System

Introduction to ER Model | Database Management System

Introduction to ER Model : The entity relationship (ER) model is a high-level data model. It is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects. It was developed to facilitate database design by allowing specification of an enterprise Schema, which represent the overall logical structure of a database. This model is based on entity relationship diagrams.

An ER Diagram is the first step towards database design. It’s a graphical methods for logical for database design. It is basically useful in design and communication of the logical database model.

Some important points regarding ER Diagrams :

  • 1976 proposed by Peter Chen
  • ER diagram is widely used in database design
  • Represent Conceptual level of a database System
  • Describe things and their relationships in high level
  • E-R model facilitates database design by allowing the specification of an “enterprise schema” which represents the overall logical structure of a database.
  • The E-R model is extremely useful in mapping the meanings and interactions of real-world enterprises onto a conceptual schema.
  • A detailed, logical representation of the entities, associations and data elements for an organization or business.

An E-R diagram naturally consists of a collection of entity sets and relationship sets and their associations. A diagram may also show the attributes and value sets that are needed to describe the entity sets and the relationship sets in the ERD. in an ERD, as shown in following figure entity sets are represented by rectangular shaped boxes. Relationships are represented by diamond shaped boxes.

 

Ellipses are used to represent attributes and lines are used to link attributes to entity sets and entity Sets to relationship sets. Consider the following E-R diagram.