Degree of relationships in DBMS and cardinality

Degree of relationships in DBMS and cardinality

1. Database
Management
System
Lecture -7

2. Relationships

3. Relationships
Relationships are the connections
and interactionsbetween 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
BOOKSTD

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
BOOKSTD
EMPPROJ

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
GRADE

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
EMPDEPT
One to many/ many to one
PROJEMP
PROJEMP
Many to many