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
Here the name attribute is partial key.
- Using attribute name relationship and age it is not possible to uniquely identify dependent.