Thursday, 14 February 2013

Entity Relationship Model and its Diagram


By on 01:26

Entity Relationship Model is the model which was introduced by P.P. chen.This model represent system data by its entity and relationships.This model is based on real world entities.

Entity Relationship Diagram(ERD):-



Component of ERD:-

1)Entity 
2)Attributes 
3)Relationship

1)Entity:-Entity is a person,place,things,object which is used to grasp,collect,stores the data.

Types  of Entity:-

a)Weak Entity Set:-Weak entity are those entity type which are not formed primary key because of insufficient attributes.

b)Strong Entity Set:-Strong entity are those entity type which are formed primary key because of sufficient attributes.

2)Attributes:-Features of entity is called as attributes example name,address etc.

Type of Attributes:-

a)Simple Attribute
b)Composite Attribute
c)Single value Attribute
d)Multivalue Attribute etc. 

3)Relationship:-Combination of two or ore than 2 entities is called as Relationship.

Type of Relationship(According to connectivity):-

a)1:1 Relationship(One to One Relationship):-One entity related to 1 entity.Example



b)1:M Relationship(One to Many Relationship):-One entity related to more than 1 entities.Example



c)M:1 Relationship(Many to One Relationship):-More than 1 entity is related with one entity set.Example Students learn in class.Example



d)M:M Relationship(Many to Many Relationship):-More than one entity associated with more than 1 entity.Example




That's all about what is ER Modelling and its tools,if you have any query then leave your comments and don't forgot to follow me on Google+,Facebook,Twitter.

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