Fill

1. Database
Management
System

2. Relationships

3. Relationships
Relationships are the connections
and interactions between the
entities instances, e.g., Program
and Student ETs are linked
How to identify relationships

4. Naming Relationships
Up to you
If there is no proper name of
the association in the system
then participants’ names of
abbreviations are used

5. Naming
STUDENT and CLASS have
ENROLL relationship
However, it can also be
named as STD_CLS

6. Symbol for Relationships
DEPT EMP
BOOK
STD

7. Relationships
Relationship type can be
identified like an entity type
A relationship type is an
abstraction of a relationship

8. Relationships
Entities involved in a relationship
are called its participants
Types of the relationships can be
established on the basis of
participant ETs

9. Relationships Types
A Binary relationship is the one
that links two entity types e.g.
STUDENT-CLASS

10. Binary Relationship Example
STD COURSE
BOOK
STD
EMP
PROJ

11. Binary Relationships
May also have instances, that can
be formally described in an
ordered pair form
 {(S1001, OS), (S1020, DS),
(S1002, DS), (S1058, NW)}

12. Attributes of the Rships
The key
The relationships can have
their descriptive attributes
Where to place

13. Attributes of Rships
STD COURSE
GRAD
E

14. Ternary Relationships
One that involves three entity
types
STUDENT-CLASS-FACULTY

15. Ternary Relationship
Examples

16. STD COURSE
FACULTY
PROJ EMP
SKILL

17. Ternary Relationships
Instances in ordered triples
Example {(S1013, MCS4,
Adnan), (S1023, MCS3,
Fasih)}

18. Unary Relationship
An ET linked with itself, also
called recursive relationship
Example Roommate, where
STUDENT is linked with
STUDENT

19. Unary Relationship Examples
STD ROOMMAT
E
EMP CHAIR-
PERSON
EMP SPOUSE

20. Cardinality of Rships
Number of instances of one
entity type that can possibly be
related to instances of other
entity type

21. Types of Cardinalities
One to one
One to many
Many to one
Many to many

22. Types of Cardinalities
DEPT
Chair
Person
One to one
EMP
DEPT
One to many/ many to one
PROJ
EMP
PROJ
EMP
Many to many

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

24. Minimum
cardinality
Maximum
cardinality

25. Cardinality Example
HOBBY
STD
BOOK
STD
COURSE
STD
PROJ
EMP
Single vertical line will show one and three line will show many and zero
will show optional i.e. it is not necessary student will issue the book.

26. Other Notations
BOOK
STD
HOBBY
STD
EMP
PROJ

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

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

29. 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

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

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

32. Roles Examples
FACULTY
STD
STD_TEACH
STD_SUP

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

34. Existence Dependency
BOOK
COPY
BOOK
bkId
bkTitle
bkId
CopyId

35. Enhancements in E-R Data Model

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

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

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

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

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