1. Database Management System
Lecture - 10

2. Minimum Cardinality
Determines whether the link is compulsory or optional
Important, since it effects the implementation

3. Cardinality Example
HOBBY
STD
BOOK
COURSE
PROJ
EMP

4. Other Notations
BOOK
STD
HOBBY
EMP
PROJ

5. Other Notations
BOOK
STD 1 M
HOBBY
EMP
PROJ

6. Other Notations
BOOK
STD 1
EMP
PROJ
CHAIR
DEPT

7. Roles in Relationships
Determine the role ETs play in a relationship
Most of the time is clear from the context, like in STD and COURSE relationship

8. Roles in Relationships
Two situation when they should be expressed explicitly
A one to one relationship
Two ETs having more than one relationship

9. Roles Examples FACUL- TY COURSE STD HEAD HEADS HEADED BY ENROLS
ENROLLED BY
ENROLMENT
FACUL- TY
HEAD
HEADS
HEADED BY

10. Roles Examples STD FACULTY Teaches Taught By Supervises Supervised by
STD_TEACH
STD_SUP
Taught By
Supervised by
Supervises
Teaches

11. Dependencies A type of constraint Existence dependency
Identifier dependency
Referential Dependency

12. Existence Dependency
BOOK
COPY
bkId
bkTitle
CopyId

13. Enhancements in E-R Data Model

14. EE-R Data Model Different proposals
Most common feature is representation of supertypes and subtypes
A popular feature of Object Oriented paradigm

15. Super/Subtypes Also called generalization/ specialization
Supertype is called a General Entity type whereas subtypes are the specializations

16. Specialized Entity Types
Super/Subtypes
PERSON
STD
FAC ST
ST1
ST3
ST2
General Entity Types
Specialized Entity Types

17. Super/Subtypes
EMP
SALARIED
HOURLY
Grade
AnalSal
NoOfHrs
HourlyRate

18. Super/Subtypes PERSON STD FAC StId CGPA Qual Grade ClsName Name Id
Address

19. Database Management System
Lecture - 10