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CS 564Database Management Systems: Design and Implementation

Lecture 1: Entity-Relationship Modeling

Chapter 2 in Cow Book

Slide ACKs: AnHai Doan, Jeff Naughton, and Jignesh Patel

Arun Kumar

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Database Design Process: ~6 steps

1. Requirements Analysis

2. Conceptual Database Design

3. Logical Database Design

4. Schema Refinement

5. Physical Database Design

6. Application and Security Design

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Database Design Process: ~6 steps

1. Requirements Analysis

2. Conceptual Database Design

3. Logical Database Design

4. Schema Refinement

5. Physical Database Design

6. Application and Security Design

EntityRelationshipModeling

RelationalModel andNormalization

Indexing, etc.

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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

Student

Name AgeSID

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ER Model Basics: Relationship

Relationship: Association among ≥ 2 entities

“Relationship Set” defined similarly

Student

Name AgeSID

Department

Name AddressDID

Major

EnrollDate

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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

s2s3

d2

d3

Department

d1s1

s4

Enroll relation:{(s1, d1), (s2, d1),(s3, d2), (s4, d3)}

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Relationships in ER

Multiple Relationships

Multiplicity of Relationships

Multi-way Relationships

Self Relationships

Multi-way to Binary Conversion

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Multiple Relationships

Student

Name AgeSID

Department

Name AddressDID

Major

Professor

Name AgePID

Advise Employ

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Multiplicity of Relationships

a2a3

b2

b3

b1a1

a4

Student DepartmentMany-to-one

a2a3

b2

b3

b1a1

a4

Professor DepartmentMany-to-many

a2a3

b2

b3

b1a1

a4

Student Citizen

One-to-one

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Many-to-One and One-to-One in ER

Student

Name AgeSID

Department

Name AddressDID

Major

Arrow: Each Student appears at most once in Enroll, i.e., given a Student, the Department is unique (no double majors!)

Student

Name AgeSID

Citizen

Name AddressDID

Match

Q: How is Many-to-Many depicted?

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CAUTION: Difference with the Book

Student

Name AgeSID

Department

Name AddressDID

Major

The Cow Book denotes the above as follows:

Student

Name AgeSID

Department

Name AddressDID

Major

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Multi-way (n-ary) Relationships

Professor

Name AgePID

Course

Name CreditsCID

Room

Number SeatsDID

Teach

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Multi-way (n-ary) Relationships

Professor

Name AgePID

Course

Name CreditsCID

Room

Number SeatsDID

TeachQ: What does this mean?

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Self Relationships

Professor

Name AgePID

Course

Name CreditsCID

Room

Number SeatsDID

Teach

Collaborate

PI Co-PI

If “roles” are different,label the edges

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Multi-way to Binary Conversion

Professor Course

Room

Teach

Professor

Course

RoomInRoom

ByProf

OfCourseTeach

Q: Why do we need these arrows?

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Apart from types of Relationships, ER

model can also capture Constraints

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Constraints in ER

Key: Uniquely identifies an entity

Participation: Total or Partial

Referential Integrity: Relationship “validity”

Single-value Constraint

Domain Constraints

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Constraints: Key

Student

Name AgeSID

Q: What does this mean?

Room

Number SeatsDID

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Constraints: Participation

Student

Name AgeSID

Department

Name AddressDID

Major

Thick: Each Professor must appear at least once in Employ

Professor

Name AgePID

Department

Name AddressDID

Employ

Q: So, what does this mean?

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Constraints: Referential Integrity

Curve: Each Professor must have a valid Department in Employ

Q: So, what does this mean?

Professor

Name AgePID

Department

Name AddressDID

Employ

Student

Name AgeSID

Department

Name AddressDID

Major

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Advanced ER Concepts

Weak Entities: an entity dependent on another

Hierarchies: “Is a” relationships among entities

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Advanced: Weak Entity

Floor

Number NumRooms

Department

Name AddressDID

PartOf

Thick/double lined shapes: Weak Entity and “dependency”

Q. Why arrow, curve, and think line from Floor to PartOf?

Q: Is a floor number ever meaningful without the Department?

DID and Number together are the Key for Floor

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Advanced: “Is A” Hierarchy

Student

Name AgeSID

Undergrad DoctoralMasters

Analogy: Sub-class Inheritance in PL

IsAIsHonors QualScore

ByThesis

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General ER Design Philosophy

1. Follow Conventions

2. Convey All App Constraints

3. Avoid Redundancy

4. Prefer Attributes over Trivial Entities

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1. Follow Conventions

Student DepartmentMajor

Student DepartmentMajor

Student DepartmentMajor

Student DepartmentMajor

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2. Convey All Application Constraints

Q. What all constraints are missing here?

Professor

Name AgePID

Department

Name AddressDID

Employ

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3. Avoid Redundancy

Student

Name AgeSID

Department

Name AddressDID

Major

DeptNAme

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4. Prefer Attributes over Trivial Entities

Student

Name AgeSID

Department

Name

Major

Student

Name AgeSID

MajorDeptName

Q. What is wrong with the above?

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Review: ER Model

1. Entity, Relationships

2. Constraints

3. Weak Entities; “IsA” Hierarchies

4. Design Philosophy