Entity Relationship model (ER model)
- The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects.
- An entity is a “thing” or “object” in the real world that is distinguishable from other objects. For example, each person is an entity, and bank accounts can be considered as entities.
- A relationship is an association among several entities. For example, a depositor relationship associates a customer with each account that she has.
- The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively.
- The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram.
Component of E-R model
The E-R model consist of the following major components:
- Key Attributes
- An entity is a class of persons, places, object, events or concepts about which we need to collect and store data.
- Each entity is distinguishable from the other entities.
- categories of different entities include:
- An attribute is a descriptive property or characteristic of an entity.
- Same attribute can be logically grouped into super attributes called compound attribute.
- Key attribute is an attribute that uniquely identifies an entity in the entity set.