Types of entities :

There are two types of entities.

1] Strong entity - An entity is a things or object in real world that is distinguishable from all other object.

• For example, every employee in the organization in an entity.

• Every entity is separated by some set of properties.

• Strong entity may have more or one properties.

• For example: employee entity can be represented by properties like employee-id, name, email, etc.

• Strong entity is represented by rectangle as

• Attribute which is used to identify entity uniquely is primary and denoted as

Weak entity - entity type that don't have key attributes of DWN are called weak entity.

entities belonging to weak type are identified by being related to specified strong entities.

• Those strong entities are called as identifying entities and relationship with weak entity is called weak relationship.

• It is represented as

Example

Here the name attribute is partial key.

• Using attribute name relationship and age it is not possible to uniquely identify dependent.