1. CS 564 Database Management Systems: Design and Implementation
Arun Kumar
Lecture 1: Entity-Relationship Modeling
Chapter 2 in Cow Book
Slide ACKs: AnHai Doan, Jeff Naughton, and Jignesh Patel

2. Database Design Process: ~6 steps
Requirements Analysis
Conceptual Database Design
Logical Database Design
Schema Refinement
Physical Database Design
Application and Security Design

3. Database Design Process: ~6 steps
Requirements Analysis
Conceptual Database Design
Logical Database Design
Schema Refinement
Physical Database Design
Application and Security Design
Entity
Relationship
Modeling
Relational
Model and
Normalization
Indexing, etc.

4. ER Model Basics: Entity
Entity: Distinguishable abstract real-world object
An entity has several “Attributes”
An attribute has a “Domain”
A collection of similar entities is an “Entity Set”
An entity set might have a “Key” attribute
SID
Name
Age
Student

5. ER Model Basics: Relationship
Relationship: Association among ≥ 2 entities
“Relationship Set” defined similarly
SID
Name
Age
DID
Name
Address
Student
Department
Major
EnrollDate

6. ER Model Basics: Relationship Set
Mathematically, given entity sets A and B, a relationship set on A and B is a subset of A X B
Student s2 s3 d2 d3
Department d1 s1 s4
Enroll relation:
{(s1, d1),
(s2, d1),
(s3, d2),
(s4, d3)}

7. Relationships in ER Multiple Relationships
Multiplicity of Relationships
Multi-way Relationships
Self Relationships
Multi-way to Binary Conversion

8. Multiple Relationships
SID
Name
Age
DID
Name
Address
Major
Student
Department
Advise
Employ
PID
Name
Age
Professor

9. Multiplicity of Relationshipsb2 b3 b1 a1 a4
Student
Department
Many-to-one a2 a3 b2 b3 b1 a1 a4
Professor
Department
Many-to-many a2 a3 b2 b3 b1 a1 a4
Student
Citizen
One-to-one

10. Many-to-One and One-to-One in ER
SID
Name
Age
DID
Name
Address
Major
Student
Department
Arrow: Each Student appears at most once in Enroll, i.e.,
given a Student, the Department is unique (no double majors!)
Student
Name
Age
SID
Citizen
Address
DID
Match
Q: How is Many-to-Many depicted?

11. The Cow Book denotes the above as follows:
CAUTION: Difference with the Book
SID
Name
Age
DID
Name
Address
Major
Student
Department
The Cow Book denotes the above as follows:
Student
Name
Age
SID
Department
Address
DID
Major

12. Multi-way (n-ary) Relationships
PID
Name
Age
CID
Name
Credits
Professor
Course
Teach
Room
DID
Number
Seats

13. Multi-way (n-ary) Relationships
PID
Name
Age
CID
Name
Credits
Professor
Course
Teach
Q: What does this mean?
Room
DID
Number
Seats

14. If “roles” are different,
Self Relationships
PID
Name
Age
CID
Name
Credits
Professor
Course
Teach PI
Co-PI
Collaborate
Room
DID
Number
Seats
If “roles” are different,
label the edges

15. Multi-way to Binary Conversion
Professor
Course
Teach
Professor
Course
Room
InRoom
ByProf
OfCourse
Teach
Room
Q: Why do we need these arrows?

16. Apart from types of Relationships, ER model can also capture Constraints

17. Constraints in ER Key: Uniquely identifies an entity
Participation: Total or Partial
Referential Integrity: Relationship “validity”
Single-value Constraint
Domain Constraints

18. Constraints: Key Student Room SID Name Age DID Number Seats
Q: What does this mean?

19. Constraints: Participation
Professor
Name
Age
PID
Department
Address
DID
Employ
Thick: Each Professor must appear at least once in Employ
Student
Name
Age
SID
Department
Address
DID
Major
Q: So, what does this mean?

20. Constraints: Referential Integrity
Professor
Name
Age
PID
Department
Address
DID
Employ
Curve: Each Professor must have a valid Department in Employ
Student
Name
Age
SID
Department
Address
DID
Major
Q: So, what does this mean?

21. Advanced ER Concepts Weak Entities: an entity dependent on another
Hierarchies: “Is a” relationships among entities

22. Advanced: Weak Entity PartOf Floor Department Number NumRooms DID Name
Address
PartOf
Floor
Department
Thick/double lined shapes: Weak Entity and “dependency”
DID and Number together are the Key for Floor
Q. Why arrow, curve, and think line from Floor to PartOf?
Q: Is a floor number ever meaningful without the Department?

23. Advanced: “Is A” Hierarchy
Analogy: Sub-class Inheritance in PL
SID
Name
Age
Student
IsA
IsHonors
QualScore
Masters
Undergrad
Doctoral
ByThesis

24. General ER Design Philosophy
Follow Conventions
Convey All App Constraints
Avoid Redundancy
Prefer Attributes over Trivial Entities

25. 1. Follow Conventions Major Student Department Major Student

26. 2. Convey All Application Constraints
PID
Name
Age
DID
Name
Address
Employ
Professor
Department
Q. What all constraints are missing here?

27. 3. Avoid Redundancy Major Student Department SID Name Age DID Name
Address
Major
Student
Department
DeptNAme

28. 4. Prefer Attributes over Trivial Entities
SID
Name
Age
Name
Major
Student
Department
Q. What is wrong with the above?
Student
Name
Age
SID
MajorDeptName

29. Review: ER Model Entity, Relationships Constraints
Weak Entities; “IsA” Hierarchies
Design Philosophy