ER Diagram

ER Model is represented by means of an ER diagram. The ER model defines the conceptual view of a database. It works around real-world entities and the associations among them. At view level, the ER model is considered a good option for designing databases.

Entity

An entity can be a real-world object that can be easily identifiable. An entity set is a collection of similar types of entities.

Attributes

Entities are represented by means of their properties, called attributes.

Types of Attributes

·         Simple attribute 

·         Composite attribute 

·         Derived attribute 

·         Single-value attribute 

·         Multi-value attribute 

Entity-Set and Keys

Key is an attribute or collection of attributes that uniquely identifies an entity among entity set.

           ·         Super Key 

           ·         Candidate Key 

           ·         Primary Key 

Relationship

The association among entities is called a relationship.

Mapping Cardinalities

       

           ·         Many-to-many 

           ·         Many-to-one 

           ·         One-to-many 

           ·         One-to-one 

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