THE ENTITY RELATIONSHIP MODEL IN DBMS.ppt

The Entity Relational Model is a model for identifying entities to be represented in the database and representation of how those entities are related. The ER data model specifies enterprise schema that represents the overall logical structure of a database graphically.

1. ENTITY RELATIONSHIP
MODEL
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2. ENTITY SETS
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An entityis an “thing” or “object” that exists in
the real world and is distinguishable from other
objects.
Example: specific person, company, event,
plant
Every entity has a set of properties i.e. the
attributes and values for those properties.
Example: people have names and addresses
An entity setis a set of entities of the same type
that share the same properties.
Example: set of all persons, companies, trees,
holidays

3. REPRESENTING ENTITIES
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ENTITY_NAME

4. EXAMPLE OF ENTITIES
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CUSTOMER
CUSTOMER_
ID
CUSTOMER_NA
ME
CUSTOMER_STR
EET
CUSTOMER_CIT
Y

5. 5
customer-id customer-customer-customer- loan-amount
name street city number
Entity Sets customerand loan

6. TYPES OF ATTRIBUTES
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SIMPLE:
COMPOSITE
MULTI VALUED:
DERIVED:

7. EXAMPLE OF ATTRIBUTES
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CUSTOMER
CUSTOMER_
ID
CUSTOMER_STR
EET
CUSTOMER_DAT
E_OF_BIRTH
NAME
LNAME
MNAMEFNAME
AGE
TELNO

8. EXAMPLE OF ATTRIBUTES
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CUSTOMER
CUSTOMER_
ID
CUSTOMER_STR
EET
CUSTOMER_DAT
E_OF_BIRTH
NAME
LNAME
MNAMEFNAME
TELNO
AGE

9. RELATIONSHIP SETS
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A relationshipis an association among several
entities
EXAMPLE: CUSTOMER HAS ACCOUNT
CUSTOMER ACCOUNT
HA
S

10. DEGREE OF A RELATIONSHIP
SET
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Referstonumberofentitysetsthatparticipatein
arelationshipset.
Relationshipsetsthatinvolvetwoentitysetsare
binary(ordegreetwo).Generally,most
relationshipsetsinadatabasesystemarebinary.

11. MAPPING CARDINALITIES
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Expressthenumberofentitiestowhich
anotherentitycanbeassociatedviaa
relationshipset.
Forabinaryrelationshipsetthemappingcardinalitymustbe
oneofthefollowingtypes:
Onetoone
Onetomany
Manytoone
Manytomany

12. ONE TO ONE ONE TO
MANY
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13. MANY TO ONE MANY TO
MANY
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14. CARDINALITY CONTRAINTS
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ONE TO ONE RELATIONSHIP

15. ONE TO MANY RELATIONSHIP
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In the one-to-many relationship a loan is
associated with at most one customer via
borrower, a customer is associated with
several (including 0) loans via borrower

16. MANY TO ONE RELATIONSHIP
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In a many-to-one relationship a loan is associated
with several (including 0) customers via borrower,
a customer is associated with at most one loan via
borrower

17. MANY TO MANY
RELATIONSHIP
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A customer is associated with several (possibly 0)
loans via borrower
A loan is associated with several (possibly 0)
customers via borrower

18. 18
PARTICIPATION OF ENTITY IN
RELATIONSHIP

19. Totalparticipation(indicated by double line): every
entity in the entity set participates in at least one
relationship in the relationship set
E.g. participation of loanin borroweris total
every loan must have a customer associated to it
via borrower
Partial participation: some entities may not participate
in any relationship in the relationship set
E.g. participation of customerin borroweris partial
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20. KEYS
PRIMARY KEY:
SUPER KEY: A super keyof an entity set is a set
of one or more attributes whose values uniquely
determine each entity.
CANDIDATE KEY:A candidate keyof an entity set
is a minimal super key
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21. ER DIAGRAM FOR
UNIVERSITY DATABASE
Draw E-Rdiagram for university database
consisting of four entities: Student, department,
Class,faculty
-student has a unique id,the student can enroll for
multiple classes
-Faculty must belong to department and faculty
can teach multiple classes
-Each class is taught by only one faculty
-Every student will get grade for the class he/she
has enrolled.
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22. WEAK ENTITY SET
An entity set that does not have a primary key is
referred to as a weak entity set.
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23. WEAK ENTITY SET
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Identifying
relationshi
p
Identifying
or owner
entity set
discriminator

24. SPECIALIZATION
The process of designating subgroupings within
an entity set.
Depicted by a trianglecomponent labeled ISA
(E.g. customer“is a” person).
Attribute inheritance–a lower-level entity set
inherits all the attributes and relationship
participation of the higher-level entity set to which
it is linked.
The ISA relationship also referred to as
superclass -subclass relationship
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26. TERNARY RELATIONSHIP
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27. EXAMPLE
Construct an E-R diagram for a
hospital with a set of patients and a
set of medical doctors. Associate
with each patient a log of the various
tests and examinations conducted.
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