1. Data Modeling and Entity-Relationship Model I
IST210
Data Modeling and Entity-Relationship Model I
IST 210: Organization of Data

2. Question: Where do relations come from?
IST210
Question: Where do relations come from?
Suppose you are now designing database for a company, how should you systematically turn user requirements into actual relations?

3. YOUR JOB! User requirement A database
IST210
I want a database to maintain departments in my company. Store information about my employees, their projects and assignments. I want ….
User requirement
$$$
YOUR JOB!
A database

4. Use Normalization Process to Design a Database?
IST210
Use Normalization Process to Design a Database?
One Approach
List all data attributes that will be involved
DepartmentName, BudgetCode, OfficeNumber, DepartPhone, EmployeeNumber, EmployeeName, EmpPhone, , ProjectID, ProjectName, …
Develop functional dependencies
EmployeeNumber  (EmployeeName, EmpPhone, )
Normalization process
Problems of this approach
Lack of a systematic approach to identify all relevant attributes

5. YOUR JOB! User requirement A database
IST210
I want a database to maintain departments in my company. Store information about my employees, their projects and assignments. I want ….
User requirement
$$$
Data Modeling
(Ch.4)
YOUR JOB!
Database Design (Ch.5)
A database

6. IST210
Two-Step Approach
Data Modeling
(Ch.4)
Database Design (Ch.5)

7. Two-Step Approach: Step 1
IST210
Two-Step Approach: Step 1
Data Modeling
(Ch.4)
Database Design (Ch.5)
Input: User requirement; Output: E-R Diagram
Use Entity-Relationship Diagram (E-R Diagram) to capture all user requirements

8. Two-Step Approach: Step 2
IST210
Two-Step Approach: Step 2
Data Modeling
(Ch.4)
Database Design (Ch.5)
Input: E-R diagram; Output: A database
Transferring a data model to a relational database
Entities  Relations
Relationships  Foreign keys and extra

9. Three Stages of Database Development
IST210
Three Stages of Database Development
Stage 1. Requirements Analysis
E-R model is a prototype of actual database system
The prototypes are used to obtain feedback from system users
Why can’t we skip stage 2?
Stage 2. Entity-Relationship Model
* Logical Stage
Stage 3. Database Design
* Physical Stage

10. Three Stages of Database Development
IST210
Three Stages of Database Development
Requirements Analysis Stage
Users are interviewed
Obtain sample forms, reports, queries, …
Component Design Stage
Create a data model
Data model: a presentation of the content, relationships, and constraints of the data needed to support the requirements
Implementation Stage
Data model transformed to database design
Database design: tables, relationships, and constraints
Database constructed and filled with data; queries, forms, and reports are created; application programs are written; and all these are tested
Users trained, documentation written, system installed for use

11. The Requirements Stage
IST210
The Requirements Stage
Sources of requirements
User Interviews
Forms
Reports
Queries
Business Rules
Use Cases
Stories/Scenarios

12. E-R Model Components E-R Models consist of Entities Relationships
Attributes
Identifiers
Relationships

13. Entities An entity is something that users want to track
IST210
Entities
An entity is something that users want to track
Customer, Order, Product
An entity instance of a specific occurrence of an entity
A customer John, an order 10021, a product A42300

14. Attributes Each attribute has a data type and properties
IST210
Attributes
An entity has attributes that describe the entity’s characteristics
Customer entity
Customer name, address, phone, home address, …
Each attribute has a data type and properties
Data type: string, number, date, …
Property: default value, value range, …

15. Identifiers Entity instances have identifiers
IST210
Identifiers
Entity instances have identifiers
An identifier will identify a particular instance in the entity class
StudentID
EmployeeID
DepartmentName
Identifier can be considered as the primary key for a relation

16. IST210
Draw an Entity
Entity Name 
Identifier 
Attributes 

17. In-Class Exercise A-1: Entity
IST210
In-Class Exercise A-1: Entity
I want a course registration database. Store information about my students, including their IDs, names, and s. A course should have information about course ID, course name, and instructor name.
How many entities do you need?
Draw a diagram for each entity using the presentation in the previous slide

18. In-Class Exercise A-1: Entity
IST210
In-Class Exercise A-1: Entity
I want a course registration database. Store information about my students, including their IDs, names, and s. A course should have information about course ID, course name, and instructor name.
STUDENT
COURSE
StudentID
CourseID
StudentName
CourseName
Instructor

19. In-Class Exercise B-1: Entity
IST210
In-Class Exercise B-1: Entity
I am the manager for apartment rental office. I want a database to maintain all my apartments. Each apartment building will have a building name, address, city, state, and zip code. A building has many apartments. An apartment has an apartment number, number of bedrooms, number of bathrooms, and monthly rent cost.
How many entities do you need?
Draw a diagram for each entity

20. In-Class Exercise B-1: Entity
IST210
In-Class Exercise B-1: Entity
I am the manager for apartment rental office. I want a database to maintain all my apartments. Each apartment building will have a building name, address, city, state, and zip code. A building has many apartments. An apartment has an apartment number, number of bedrooms, number of bathrooms, and monthly rent cost.
BuildingID
Name
Address
City
State
Zip
BUILDING
BuildingID
ApartmentID
NumberOfBed
NumberOfBath
Rent
APARTMENT

21. E-R Model Components E-R Models consist of Entities Relationships
Attributes
Identifiers
Relationships

22. IST210
Relationships
Entities can be associated with one another in relationships
Relationship degree defines the number of entity classes participating in the relationship
Degree 2 is a binary relationship
A relationship connects two entities
Most common relationship
Our course will only use binary relationship
Degree 3 is a ternary relationship
Degree 1 is a recursive (unary) relationship

23. Degree 2 Relationship: Binary
IST210
Degree 2 Relationship: Binary
BUILDING
STUDENT
Have
Register
APARTMENT
CLASS

24. Degree 3 and Degree 1 Relationship
IST210
Degree 3 and Degree 1 Relationship
USER
Friending
Our course will only use binary relationship (relationship between two entities)

25. Relationship Cardinality
IST210
Relationship Cardinality
Relationships are named and classified by their cardinality, which is a word that means count
Maximum Cardinality
One-One, One-Many, Many-Many
Minimum Cardinality
Optional, Mandatory

26. IST210
Maximum Cardinality
Maximum cardinality is the maximum number of entity instances that may participate in a relationship instance — one, many or other some fixed number

27. One-to-One Relationship
IST210
One-to-One Relationship
1:1 (one-to-one)
A single entity instance in one entity class is related to a single entity instance in another entity class
An employee may have no more than one locker
A locker may only be accessible by one employee

28. One-to-Many Relationship
IST210
One-to-Many Relationship
1:N (one-to-many)
A single entity instance in one entity class is related to many entity instances in another entity class
A video in YouTube is uploaded by one user
A user may upload several videos
UPLOAD
1:N
USER
VIDEO

29. Many-to-Many Relationship
IST210
Many-to-Many Relationship
N:M (many-to-many)
Many entity instances in one entity class is related to many entity instances in another entity class
A YouTube user may subscribe several channels
A particular channel may be subscribed by several users
SUBSCRIBE
N:M
USER
CHANNEL

30. Maximum Cardinality: Crow’s Foot Notation
IST210
Maximum Cardinality: Crow’s Foot Notation
One
Many (crow’s foot)
An employee has (at most) one locker; a locker can belong to (at most) one employee
EMPLOYEE
LOCKER
A user can upload many videos; a video can be uploaded by (at most) one user
USER
VIDEO
Attention: do not misplace one and many notations
A user can subscribe to many channels; a channel can be subscribed by many users
USER
CHANNEL

31. Maximum Cardinality: Exercise
IST210
Maximum Cardinality: Exercise
How to determine maximum cardinality? (1) user requirement; (2) common sense
Which design is most suitable?
upload
(A)
USER
VIDEO
(B)
USER
VIDEO
USER
VIDEO
(C)
USER
VIDEO
(D)

32. Maximum Cardinality: Exercise
IST210
Maximum Cardinality: Exercise
How to determine maximum cardinality? (1) user requirement; (2) common sense
Which design is most suitable?
subscribe
(A)
USER
CHANNEL
(B)
USER
CHANNEL
USER
CHANNEL
(C)
USER
CHANNEL
(D)

33. In-Class Exercise: Maximum Cardinality
IST210
In-Class Exercise: Maximum Cardinality
In-Class Exercise A-2
Draw a line between STUDENT and COURSE
Draw the Maximum Cardinality on the line using Crow’s foot notation
In-Class Exercise B-2
Draw a line between BUILDING and APARTMENT
Draw the Maximum Cardinality on the line using Crow’s foot notation

34. In-Class Exercise: Maximum Cardinality
IST210
In-Class Exercise: Maximum Cardinality
In-Class Exercise A-2
Draw a line between STUDENT and COURSE
Draw the Maximum Cardinality on the line using Crow’s foot notation
STUDENT
COURSE
StudentID
CourseID
StudentName
CourseName
Instructor

35. In-Class Exercise: Maximum Cardinality
IST210
In-Class Exercise: Maximum Cardinality
In-Class Exercise B-2
Draw a line between BUILDING and APARTMENT
Draw the Maximum Cardinality on the line using Crow’s foot notation
BUILDING
APARTMENT
BuildingID
BuildingID
ApartmentID
Name
Address
City
State
Zip
NumberOfBed
NumberOfBath
Rent

36. IST210
Minimum Cardinality
Minimum cardinality is the minimum number of entity instances that must participate in a relationship instance
These values typically assume a value of zero (optional) or one (mandatory)
Crow’s foot notation
Mandatory
Optional

37. Minimum Cardinality Mandatory Optional
IST210
Minimum Cardinality
Mandatory
Optional
Minimum cardinality notation is closer to the middle
An employee may have a locker; a locker must belong to an employee
EMPLOYEE
LOCKER
Maximum cardinality notation is closer to entity

38. Minimum Cardinality: Crow’s Foot Notation
IST210
Minimum Cardinality: Crow’s Foot Notation
Mandatory
Optional
An employee must have a locker; a locker must belong to an employee
EMPLOYEE
LOCKER
An employee must have a locker; a locker may belong to an employee
EMPLOYEE
LOCKER
An employee may have a locker; a locker must belong to an employee
EMPLOYEE
LOCKER
An employee may have a locker; a locker may belong to an employee
EMPLOYEE
LOCKER

39. Minimum Cardinality: Exercise
IST210
Minimum Cardinality: Exercise
Mandatory
Optional
USER
VIDEO
What does the cardinality mean?
(A) A user must upload many videos; a video may belong to a user
(B) A user may upload many videos; a video must belong to a user
(C) A user may upload many videos; a video may belong to a user
(D) A user must upload many videos; a video must belong to a user

40. Minimum Cardinality: Exercise
IST210
Minimum Cardinality: Exercise
How to determine Minimum cardinality? (1) user requirement; (2) common sense
Which design is most suitable?
upload
(A)
USER
VIDEO
(B)
USER
VIDEO
USER
VIDEO
(C)
USER
VIDEO
(D)

41. Minimum Cardinality: How to determine?
IST210
Minimum Cardinality: How to determine?
How to determine minimum cardinality?
user requirement;
common sense
In most cases, the minimum cardinalities are optional, unless one entity is dependent on another entity
Example: A video cannot be uploaded without a user; a user can exist without uploading a video

42. Minimum Cardinality: How to determine? (cont.)
IST210
Minimum Cardinality: How to determine? (cont.)
* We will never have mandatory – mandatory relationship. Why?
An employee must have a locker; a locker must belong to an employee
EMPLOYEE
LOCKER
This design looks fine.But it will cause problem when you insert data records!
When you insert a new data record on employee A,
he must already have an assigned locker B.
But when you insert the locker B,
it must already be assigned to employee A.
So, one cannot be inserted without the other one already exists! Conflict!

43. Minimum Cardinality: Exercise
IST210
Minimum Cardinality: Exercise
How to determine minimum cardinality? (1) user requirement; (2) common sense
Which design is most suitable?
subscribe
(A)
USER
CHANNEL
(B)
USER
CHANNEL
(C)
USER
CHANNEL
(D)
USER
CHANNEL

44. In-Class Exercise: Minimum Cardinality
IST210
In-Class Exercise: Minimum Cardinality
In-Class Exercise A-3
Add Minimum Cardinality symbols on the line of the relationship
STUDENT
COURSE
StudentID
CourseID
StudentName
CourseName
Instructor

45. In-Class Exercise: Minimum Cardinality
IST210
In-Class Exercise: Minimum Cardinality
In-Class Exercise B-3
Add Minimum Cardinality symbols on the line of the relationship
BUILDING
APARTMENT
BuildingID
BuildingID
ApartmentID
Name
Address
City
State
Zip
NumberOfBed
NumberOfBath
Rent

46. Multiple Relationships between Entities
IST210
Multiple Relationships between Entities
STUDENT
CLUB
StudentID
president
ClubID
Name
ClubName
Description
member
Sometimes, there could multiple relationships with different semantic meanings between two entities. In the above example, a club will have a student as the president. Students can also become the members of the club.

47. Multiple Relationships between Entities
IST210
Multiple Relationships between Entities
USER
PRODUCT
UserID
Sell
ProductID
Name
Name
Description
Buy
A product must be sold by a user. A user could also buy many products.

48. Crow’s Foot Symbols: Summary
IST210
Crow’s Foot Symbols: Summary
In our course, we will use Crow’s foot notation to represent the maximum and minimum cardinalities of relationships
Mandatory
Optional
Minimum cardinality
USER
VIDEO
Maximum cardinality
One
Many

49. E-R Diagram E-R Diagram: Entity-Relationship Diagram
IST210
E-R Diagram
E-R Diagram: Entity-Relationship Diagram
(1) entity; (2) identifier; (3) attributes; (4) relationship
A complete E-R Diagram represented using Crow’s Foot notation
In this E-R diagram, there are two entities and one relationship
USER
VIDEO
UserID
Video ID
Name
Address
Title
Description
Length
upload

50. Summary Entity Attributes Identifier Relationship
IST210
Summary
Entity
Attributes
Identifier
Relationship
Maximum cardinality
One, many
Minimum cardinality
Optional, mandatory
Know how to use Crow’s foot notations to draw an E-R diagram