ER Model is a popular high-level (conceptual) data model. It is an approach to designing Semantic Conceptual schema of a Database. ER model allows us to describe the data involved in a real-world environment in terms of objects and their relationships, which are widely used in design of database. ER model provides preliminary concepts or idea about the data representation which is later modified to achieve final detailed design.
Important concepts/notions used in ER modeling are-
Entity
It is an object in real-world or some idea or concept which can be distinguished from other objects.
Ex.: person, school, class, department, weather, salary, temperature etc.
Entity has independent existence.
Entity type
Each entity belongs to an Entity type that defines the structure.
Entity Set
It is a Collection of similar objects.
Attribute
Reflects a property of an object or entity. We have following types of attributes.
> Simple attribute
> Composite attribute
> Single valued attribute
> Multi-valued attribute
> Derived attribute
> Stored attribute
Key
Is an Attribute of an entity type whose value can uniquely identify an entity in a set.
Relationship
The association between entities is known as relationship.
Domain of an attribute
The set of possible values is known as domain of an attribute
