Entity Relationship Model is the model which was introduced by P.P. chen.This model represent system data by its entity and relationships....
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):-
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):-
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
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