Minimum Cardinality and roles in relationship and dependencies

1. Database
Management
System
Lecture - 08

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

3. Cardinality Example
HOBBY
STD
BOOK
STD
COURSE
STD
PROJ
EMP

4. Other Notations
BOOK
STD
HOBBY
STD
EMP
PROJ

5. Other Notations
BOOK
STD 1 M
HOBBY
STD 1
M
EMP
PROJ M
M

6. Other Notations
BOOK
STD 1
EMP
PROJ
CHAIR
DEPT 1
1

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
COURSE
STD ENROLS ENROLLED
BY
ENROLMENT
FACUL-
TY
HEAD
HEADS
HEADED BY

10. Roles Examples
FACULTY
STD
STD_TEACH
STD_SUP

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

12. Existence, Referential
Dependency
BOOK
COPY
BOOK
bkId
bkTitle
bkId
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. 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