It is a conceptual modelling tool which represents data in the form of entities and relationalships.
Entity: An entity is a object or concept in which information is stored and represented by rectangles.It is something which can be defined.like person,object. Entities are nouns.
Actions: These are represented by diamond shape and depitics how two entities share information in database.
Attribute: It is a property,characteristic of an entity ,relationship or any other attribute.
Relationalship: It describes how entities interact.
It describes the numerical attributes of a relationship between two entities. It is of three types
One to one: example: customer with one login ID
One to many:one student registering multiple courses
Many to many: students associated with many lecturers.
To draw ER diagrams:
Identify all the entities in a system.Any entity should appear once in a ER diagram.All the entities should be placed in rectangle and named properly.
Identify relationships between entities and connect entities using line and diamond shape for actions describing relationalship.
Add attributes for entities.
Example of ER diagram
Benefits for ER diagram
They easily communicate with developers,end users and customers.They can translate into relational tables which helps to build databases.