What is Entity relationship model(E-R model)[DBMS-1]

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Entity relationship model(E-R model)

-Entity relationship model consists of the entities and relationship.
-It was developed to facility database designed by allowing specification of the enterprise schema.
-the enterprise schema consists of the overall logical structure of the database.
-The E-R model is very useful  in mapping the meaning integration of the recall world enterprise on the conceptual schema.
-The E-R data model is three basic option :
       _Entity set
       _relationship set
       _Attributes  
-It is use for the conceptual design of the database application.

Entity: 

An object which has a some physical existence is called entity.

Relationship:

A relationship is a associate among several entity.

Entity set are relationship set

Entity set:

-A group of similar types of entities is called is called entity sets.
-Let T be a entity set e1,e2,e3..........en.
  e1,e2,e3,,,,,,,,en are the same types of entity.
-Or a entity set is a set of entity of the same type that can share the some properties.
-The individual entity constitute a set are said to be the extension of the entity set.
-ex the set of all the persons who are customer at given bank that can define as extension of the entity set customer.
-All individual bank customer are the extension of the entity set customer.
-The entity set does not need disjoint .
                                                      (Entity set of customer and loan)

Relationship sets:

-A relationship is a associate among several entity.
-A group of relationship is known as relationship sets.
-ex a relationship that associate customer with the loan L17 and this is specific relationship that is  customer with loan L17.
-We can have more than one relationship that can be define the overall same entity.
-A relationship set is a set of relationship of the same type.
-Formally it is mathematically origination no N>2 entity set.
-It is a entity set e1,e2,e3........en
  than the relationship R is a subset of e1,e2,e3.....en.

Attributes:

-Properties or characteristics of the entity is called attributes. 
 attributes are the descriptive properties 
 proceed by the each member of the entity set.
-ex the possible attributes of the customer entity are the customer id ,customer city ,loan.
-there are the 4 types of attribute:
                                                     -single value and multi value attributes
                                                     -simple and composite attributes 
                                                     -derived attributes
                                                     -null attributes 

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