E-R Diagram

An entity relationship diagram (ERD) is a graphical representation of different information which shows the entity ie. people, objects, places, concepts or events and their relationship. Its shows the information stored in a database. In other word, it is a graphical representation database. It also provides the means of communication. The logical structure of database can be expressed graphically by an E-R diagram. It uses following component to built up E-R diagram:

⬜     It represents entity. 
◯      It represents relationship among entities.       
♢     It represents attributes of entities. 
─     It is used to show the link of attributes to entities and                        entities to relationship and vice versa. 

Fig: An E-R diagram for the relationship Customer Orders Item

Entity, Attribute and Relationship

Entity:

An entity is a name of ‘thing’ or ‘person’ or ‘object’ in the real world. Students, employee, house, table etc are the example of entity. 

Attribute:

The properties that characterize an entity set are called its attribute. Customer_id, student_no, etc. are the example of attributes. 

Relationship:

The association between entities is called relationship. Customer order item, Harry reads books etc. are the example of relationship.