Entity and Entity Relationship model
ER or Entity Reletionship model is used to create and model the data which is simple, non technical and easily understood by people describing a diagram with relation. It helps us to analyze requirements systematically to produce a well designed database.
It is a visual representation of entity and attributes also it helps us to show relationships between entities . Symbols and connectors are used to indicate the relation between entities or describe information using symbols and connectors.
Entity type: It defines a collection of similar entities.
Types of entity type are as follows:
- Strong entity: Strong entity means an entity which has primary key and it doesn’t depend on other entities for existence. It is also known a parent entity.
- Weak entity: Weak entity means an entity which doesn’t have key attributes of their own.
- Composite entity: Composite entity is used to make a Many to Many relationship between 2 or more entities. This entity is composed of primary keys from each of the connected entities.
- Recursive entity: When an entity has a relation with same entity it is called recursive entity.