Lecture 7 (Week 7) - Cardinality & modality.pptx

“Database Management Systems”
CS-222
Lecture 33
“Cardinality & modality”
Dr. Muhammad Muneer Umar
By:
Lecturer in Computer Science
Institute of Computing
KUST, Pakistan

Consider some cases
• An employee can have many children
• A student must have exactly one father
• Many teachers are teaching many subjects
Course: Database Management Systems (CS222) || Instructor: Dr. Muneer Umar, Lecturer. Institute of Computing, KUST || Email: muneer.umar@kust.edu.pk
Topic: Cardinality & Modality

Agenda
• Revision of ERD
• Cardinality and Modality
• How to read cardinalities
• Sample Cases

-Semantic Data Model
-Graphical representation of the conceptual
database design
ERD ( Entity Relationship Diagram)

-Semantic Data Model
-Graphical representation of the conceptual
database design
Three major constructs:
1.Entity
2.Attributes
3.Relationships
ERD ( Entity Relationship Diagram)

Entity
Entity
Type
Entity
Instance
Entity
Set

STUDENT LOCATION
1.Entity-Entity Type

STUDENT LOCATION
Name … ZIP
Ali --- 26000
Ahmed --- 25000
ZIP City Province Country
26000 Kohat KPK Pakistan
25000 Peshawar KPK Pakistan
41000 Islamabad Pakistan
1.Entity-Entity Instance & Set

STUDENT
2. Attributes
Name
FName
Age
Skills
Skills
Session
Start End

STUDENT LOCATION
Name … ZIP
Ali --- 26000
Ahmed --- 25000
Khan --- 26000
54000 Lahore Punjab Pakistan
72206 Tehran Tehran Iran
3. Relationships

STUDENT LOCATION
Name … ZIP
Ali --- 26000
Ahmed --- 25000
Khan --- 26000
3. Relationships

Cardinality  Maximum possible
associations
1 OR many
Modality  Minimum possible
associations
1 OR Zero

STUDENT LOCATION
Name … ZIP
Ali --- 26000
Ahmed --- 25000
Khan --- 26000
Modality
Cardinality

Cardinality and Modality
Cardinality and Modality work together to define the relationship
• Cardinality indicates the maximum number of times an
instance in one entity can be associated with instances in the
related entity
• Modality indicates the minimum number of times an instance
in one entity can be associated with an instance in the related
entity
• Cardinality and Modality are both shown on the relationship
line by symbols

Reading Modality and Cardinality
from Zero to Many
from One to Many
from One to One
i.e., one and only one
from Zero to One
Modality and cardinality are combined (two at a time)
in these ways:

Student
Seat
fills
Course
Instructor teaches
Course
Student Registers
for
Transcript
Student
has
Left to right: a seat is filled by exactly one student
Right to left: a student fills exactly one seat
Left to right: a student has one or more transcripts
Right to left: a transcript has one student
Left to right: a student registers for one or more courses
Right to left: a course is registered by one or more students
Left to right: an instructor teaches zero to many courses
Right to left: a course is taught by exactly one instructor
Reading Cardinality and Modality

Student
Seat
fills
Course
Instructor teaches
Course
Student Registers
for
Left to right: one to one, 1:1
Right to left: one to one, 1:1
Left to right: one to many, 1:M
Right to left: many to one, M:1
Left to right: many to many, M:M
Right to left: many to many, M:M
Left to right: one to many, 1:M
Right to left: many to one, M:1
Reading Cardinality
Transcript
Student
has

Cardinalities and Modalities
•Modalities can also be called as:
•Mandatory Cardinalities = The entity must
participate in another entity.
•Optional Cardinalities = The entity has the
option to participate in another entity.

Cardinalities and Modalities
•Cardinalities and modalities can also be
defined as:
•Maximum Cardinality: One or many
•Minimum Cardinality: Required or not.

EMPLOYEE VEHICLE
Name … VID
Ali --- IDE403
Ahmed ---
Khan --- EGA911
Akbar CSS900
Burhan ACX907
VID Type Model Maker
IDE403 Sedan 2017 Toyota
ACX907 Hatchback 2013 Suzuki
EGA911 SUV 2009 Toyota
CSS900 Sedan 2011 Toyota
Is it Correct??

EMPLOYEE VEHICLE
Name … VID
Ali --- IDE403
Ahmed ---
Khan --- EGA911
Akbar CSS900
Burhan ACX907
VID Type Model Maker
IDE403 Sedan 2017 Toyota
ACX907 Hatchback 2013 Suzuki
EGA911 SUV 2009 Toyota
CSS900 Sedan 2011 Toyota
Now it is Correct 

EMPLOYEE CHILDREN
Name … CID
Ali --- C001
Ali --- C002
Khan --- C003
Akbar
Burhan C004
CID NAME ---
C001 Asad
C002 Ayesha
C003 Farooq
C004 Khalil
???

SUMMARY
• REVISION OF ERD
• Cardinality  Maximum cases (1 or many)
• Modality  Minimum Cases (0 or 1)
• Mandatory Cardinality  Modality =1
• Optional Cardinality  Modality = 0
• Possible Cases  1:1, 1:M, M:M (can be read from both direction)

Thank You
•You any query post your comment on KCMS.

Lecture 7 (Week 7) - Cardinality & modality.pptx

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Lecture 7 (Week 7) - Cardinality & modality.pptx