Dbms Notes Lecture 9 : Specialization, Generalization and Aggregation

Specialization, Generalization and aggregation in E R Diagram

1. UNIT 1
Lecture 9
EER Model

2. Extended E R Model
1.Specialization
2.Generalization
3.AttributeInheritance
4.Aggregation
Dinesh Kumar Bhawnani, BIT DURG

3. Specialization
•Theprocessofdesignatingsub-groupingsor
dividingahigherlevelentitysetintoanumberof
lowerlevelentitysetonthebasisofspecific
featuresisknownasspecialization.
•ItisanTop–Downapproach.
Dinesh Kumar Bhawnani, BIT DURG

4. Generalization
•Theprocessofgroupingorjoiningtwoormorelower
levelentitysetstomakeahigherlevelentityseton
thebasisoftheircommonfeaturesisknownas
generalization.
•It is an Bottom –Up approach.
Dinesh Kumar Bhawnani, BIT DURG

5. Specialization/ Generalization
•IntermsofanE-Rdiagram,specializationisdepictedbya
trianglecomponentlabeledISA.
•TheISArelationshipmayalsobereferredtoasasuperclass-
subclassrelationship.
•Higherandlower-levelentitysetsaredepictedasregular
entitysetsi.e.,asrectanglescontainingthenameofthe
entityset.
Dinesh Kumar Bhawnani, BIT DURG

6. Generalization/ Specialization
Dinesh Kumar Bhawnani, BIT DURG
PERSON
ISA
CUSTOMER EMPLOYEE
Name
Street
City
Cust_id Emp_id
Salary

7. Generalization/ Specialization
Dinesh Kumar Bhawnani, BIT DURG
ACCOUNT
ISA
CHECKING-ACCOUNT SAVINGS-ACCOUNT
Acc_No
Balance
Overdraft_Amount Interest_Rate

8. Generalization/ Specialization
Dinesh Kumar Bhawnani, BIT DURG
STUDENT
ISA
UNDER-GRADUATE POST-GRADUATE
Stud_Id
Stud_Name
Discipline
Specialization

9. Difference
No. Specialization Generalization
1It is a Top Down approach. It is a Bottom Up approach.
2Specialization stems from a single entity set;
it emphasizes differences among entities
within the set by creating distinct lower-
level entity sets.
Generalization proceeds from the recognition
that a number of entity sets share some
common features (namely, they are described
by the same attributes and participate in the
same relationship sets).
3The process of designating sub-groupings
within an entity set is called specialization.
The process of designating groupings from
various entity sets is called generalization.
4Specialization is a result of taking a subset
of higher level entity set to form a lower-
level entity set.
Generalization is a result of taking the union of
two or more disjoint (lower-level) entity sets to
produce a higher-level entity set.
Dinesh Kumar Bhawnani, BIT DURG

10. Attribute Inheritance
•Acrucialpropertyofthehigherandlower-level
entitiescreatedbyspecializationandgeneralizationis
attributeinheritance.
•Theattributesofthehigher-levelentitysetsaresaid
tobeinheritedbythelower-levelentitysets.
Dinesh Kumar Bhawnani, BIT DURG

11. Constraints on Specialization/ Generalization
•Condition-defined.Incondition-definedlower-
levelentitysets,membershipisevaluatedonthe
basisofwhetherornotanentitysatisfiesan
explicitconditionorpredicate.
•User-defined.User-definedlower-levelentity
setsarenotconstrainedbyamembership
condition;rather,thedatabaseuserassigns
entitiestoagivenentityset.
Dinesh Kumar Bhawnani, BIT DURG

12. Condition -Defined
Dinesh Kumar Bhawnani, BIT DURG
ACCOUNT
ISA
CHECKING-ACCOUNT SAVINGS-ACCOUNT
Acc_No
Balance
Overdraft_Amount Interest_Rate
Account_Type

13. Dinesh Kumar Bhawnani, BIT DURG
PERSON
ISA
EMPLOYEE
Name
Street
City
CUSTOMER
Salary Credit_Rating
ISA
OFFICER SECRETARYTELLER
Officer_No
Station_No
Hours_Worked
Hours_Worked
User -Defined

14. Constraints on Specialization/ Generalization
•Asecondtypeofconstraintrelatestowhetherornotentitiesmay
belongtomorethanonelower-levelentitysetwithinasingle
generalization.Thelower-levelentitysetsmaybeoneofthe
following:
•Disjoint.Adisjoint-nessconstraintrequiresthatanentitybelongto
nomorethanonelower-levelentityset.
•Overlapping.Inoverlappinggeneralizations,thesameentitymay
belongtomorethanonelower-levelentitysetwithinasingle
generalization.
•Lower-levelentityoverlapisthedefaultcase;adisjoint-ness
constraintmustbeplacedexplicitlyonageneralization(or
specialization).WecannoteadisjointednessconstraintinanE-R
diagrambyaddingtheworddisjointnexttothetrianglesymbol.
Dinesh Kumar Bhawnani, BIT DURG

15. Disjoint Constraint
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ACCOUNT
ISA
CHECKING-ACCOUNT SAVINGS-ACCOUNT
Acc_No
Balance
Overdraft_Amount Interest_Rate
Account_Type
disjoint

16. Dinesh Kumar Bhawnani, BIT DURG
PERSON
ISA
EMPLOYEE
Name
Street
City
CUSTOMER
Salary Credit_Rating
ISA
OFFICER SECRETARYTELLER
Officer_No
Station_No
Hours_Worked
Hours_Worked
Overlapping

17. Constraints on Specialization/ Generalization
•Afinalconstraint,thecompletenessconstraintonageneralizationor
specialization,specifieswhetherornotanentityinthehigher-levelentity
setmustbelongtoatleastoneofthelower-levelentitysetswithinthe
generalization/specialization.Thisconstraintmaybeoneofthefollowing:
•Totalgeneralizationorspecialization.Eachhigher-levelentitymustbelong
toalower-levelentityset.
•Partialgeneralizationorspecialization.Somehigher-levelentitiesmaynot
belongtoanylower-levelentityset.
•Partialgeneralizationisthedefault.
•WecanspecifytotalgeneralizationinanE-Rdiagrambyusingadouble
linetoconnecttheboxrepresentingthehigher-levelentitysettothe
trianglesymbol.
Dinesh Kumar Bhawnani, BIT DURG

18. Total Specialization/ Generaliztion
Dinesh Kumar Bhawnani, BIT DURG
ACCOUNT
ISA
CHECKING-ACCOUNT SAVINGS-ACCOUNT
Acc_No
Balance
Overdraft_Amount Interest_Rate
Account_Type

19. Dinesh Kumar Bhawnani, BIT DURG
PERSON
ISA
EMPLOYEE
Name
Street
City
CUSTOMER
Salary Credit_Rating
ISA
OFFICER SECRETARYTELLER
Officer_No
Station_No
Hours_Worked
Hours_Worked
Partial

20. Aggregation
•OnelimitationoftheE-Rmodelisthatitcannot
expressrelationshipsamongrelationships.
•Aggregationisanabstractionthroughwhich
relationshipsaretreatedashigherlevelentities.
Dinesh Kumar Bhawnani, BIT DURG

21. ER Diagram with redundant relationships
Dinesh Kumar Bhawnani, BIT DURG
JOB
EMPLOYEE BRANCH
MANAGER
works-on
manages

22. ER diagram with Aggregation
Dinesh Kumar Bhawnani, BIT DURG
MANAGER
manages
JOB
EMPLOYEE BRANCHworks-on

23. Draw the ER diagram for a banking enterprise
Dinesh Kumar Bhawnani, BIT DURG

24. Dinesh Kumar Bhawnani, BIT DURG
E R Diagram Notations

25. University Questions
1.Write short notes on
1.Generalization
2.Specialization
3.Disjoint and overlapping constraints
4.Condition defined and user defined constraints
5.Total and partial generalization
2.Explain the constraints based on generalization and specialization.
3.Differentiate between specialization and generalization.
4.Explain aggregation with example.
5.Explain enhanced entity set model with examples.
Dinesh Kumar Bhawnani, BIT DURG

26. For Video lecture on this topic please subscribe to my youtubechannel.
The link for my youtubechannel is
https://www.youtube.com/channel/UCRWGtE76JlTp1iim6aOTRuw?sub
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Dinesh Kumar Bhawnani, BIT DURG