Entity Relational Model

 The Entity Relational Model is a model for identifying entities to be represented in the database and representation of how those entities are related. The ER data model specifies enterprise schema that represents the overall logical structure of a database graphically. 

The Entity Relationship Diagram explains the relationship among the entities present in the database. ER models are used to model real-world objects like a person, a car, or a company and the relation between these real-world objects. In short, ER Diagram is the structural format of the database. 

Why Use ER Diagrams In DBMS?

• ER diagrams are used to represent the E-R model in a database, which makes them easy to be converted into relations (tables).
• ER diagrams provide the purpose of real-world modeling of objects which makes them intently useful.
• ER diagrams require no technical knowledge and no hardware support.
• These diagrams are very easy to understand and easy to create even for a naive user. 
• It gives a standard solution for visualizing the data logically.

Symbols Used in ER Model

ER Model is used to model the logical view of the system from a data perspective which consists of these symbols:

• Rectangles: Rectangles represent Entities in ER Model.
• Ellipses: Ellipses represent Attributes in ER Model.
• Diamond: Diamonds represent Relationships among Entities.
• Lines: Lines represent attributes to entities and entity sets with other relationship types.
• Double Ellipse: Double Ellipses representMulti-Valued Attributes.
• Double Rectangle: Double Rectangle represents a Weak Entity.