Entity Relationship Modeling

Introduction to ER Model

ER Model is a high-level data model, developed by Chen in 1976. This model defines the data elements and relationships for a specified system. It is useful in developing a conceptual design for the database & is very simple and easy to design logical view of data.

Importance of ER Model

  • ER Model is plain and simple for designing the structure.
  • It saves time.
  • Without ER diagrams you cannot make a database structure & write production code.
  • It displays the clear picture of the database structure.

ER Diagrams

  • ERD stands for Entity Relationship diagram.
  • It is a graphical representation of an information system.
  • ER diagram shows the relationship between objects, places, people, events etc. within that system.
  • It is a data modeling technique which helps in defining the business process.
  • It used for solving the design problems.
Following are the components of ER Diagram,

rectangleRectangleIt represents the Entity.
ellipseEllipseIt represents the Attribute.
diamondDiamondIt represents the Relationship.
lineLineIt represents the link between attribute and entity set to relationship set.
double rectangleDouble RectangleIt represents the weak entity.
composite attributeComposite AttributeIt represents composite attribute which can be divided into subparts.
For eg. Name can be divided into First Name and Last Name
multi valued attributeMulti valued AttributeIt represents multi valued attribute which can have many values for a particular entity. For eg. Mobile Number.
derived attributeDerived AttributeIt represents the derived attribute which can be derived from the value of related attribute.
key attributeKey AttributeIt represents key attribute of an entity which have a unique value in a table.
For eg. Employee → EmpId (Employee Id is Unique).