1. Yong Choi School of Business CSUB
MIS 340: Data Modeling 1
Yong Choi
School of Business
CSUB

2. Study Objectives Understand concepts of data modeling and its purpose
Learn how relationships between entities are defined and refined, and how such relationships are incorporated into the database design process
Learn how ERD components affect database design and implementation
Learn how to interpret the modeling symbols

3. Why Data Modeling? Represent “reality” of the actual database
Blue print: documentation
Effective Communication Tool
User involvement
Represent abstraction of requirements
Identify the business rules to be stored in the database
Independence from a particular DBMS

4. Conceptual data modeling
The conceptual data modeling revolves around discovering and analyzing organizational and users data requirements (see the supplement).
What data is important
What data should be maintained
The major activity of this phase is identifying entities, attributes, and their relationships to construct model using the Entity Relationship Diagram methodology. 7

5. Entity Relationship diagram (ERD)
Data modeling methodology
Developed by Peter Chen (1976).
See his original ERD article on the class website
ERD is commonly used to:
Translate different views of data among managers, users, and programmers to fit into a common framework.
Define data processing and constraint requirements to help us meet the different views.
Help implement the database. 16

6. Basic ERD Elements
Entity : a collection of people, places, objects, events, concepts of interest (a table)
Entity instance – a member of the Entity : a person, a place, an object … (a row in a table)
Attribute - property or characteristic of interest of an entity (a field in a table)
Relationship – association between entities (corresponds to primary key-foreign key equivalencies in related tables) 2

7. ERD using Chen’ Notation (first - original)

8. Chen’s Notation Entities Attributes Relationships
rectangle containing the entity’s name.
Attributes
oval containing the attribute’s name.
Relationships
diamond containing the relationship’s name. 17

9. Steps for creating an ERD
Identify entities
Identify attributes
Identify relationships

10. Entity
“A fundamental THING of relevance to the enterprise about which data may be kept”
What should be an Entity: both tangible & intangible
An object that will have many instances in the database
An object that will be composed of multiple attributes
An object that we are trying to model
What should NOT be an Entity:
A user of the database system
An output of the database system (e.g. a report)

11. ERD using IE Notation (most popular)

12. Entity Instance Student ID Last Name First Name 2144 Arnold Betty 3122
Entity instance: a single occurrence of an entity.
6 instances
Student ID
Last Name
First Name
2144
Arnold
Betty
3122
Taylor
John
3843
Simmons
Lisa
9844
Macy
Bill
2837
Leath
Heather
2293
Wrench
Tim
Entity: student
instance

13. Entity Instance (con’t)

14. Attributes “describe property or characteristic of an entity ”
Entity: Employee
Attributes:
Employee-Name
Address (composite)
Phone Extension
Date-Of-Hire
Job-Skill-Code
Salary 18

15. Classes of attributes Simple attribute Composite attribute
Derived attributes
Single-valued attribute
Multi-valued attribute 5

16. Simple/Composite attribute
A simple attribute cannot be subdivided.
Examples: Age, Gender, and Marital status
A composite attribute can be further subdivided to yield additional attributes.
Examples:
ADDRESS -- Street, City, State, Zip
PHONE NUMBER -- Area code, Exchange number 22

17. Derived attribute is not physically stored within the database
instead, it is derived by using an algorithm.
Example: AGE can be derived from the date of birth and the current date.
MS Access: int(Date() – Emp_Dob)/365) 22

18. Single-valued attribute
can have only a single (atomic) value.
Examples:
A person can have only one social security number.
A manufactured part can have only one serial number.
A single-valued attribute is not necessarily a simple attribute.
Part No: CA
Location: CA, Factory#:08, shift#: 02, part#: 23

19. Multi-valued attributes
can have many values.
Examples:
A person may have several college degrees.
A household may have several phones with different numbers
A car color 23

20. Example - “Movie Database”
Entity:
Movie Star
Attributes:
SS#: “ ” (single-valued)
Cell Phone: “(661) , (661) ” (multi-valued)
Name: “Harrison Ford” (composite)
Address: “123 Main Str., LA, CA” (composite)
Birthdate: “1-1-50” (simple)
Age: 50 (derived)

21. How to find entities? Entity:
A fundamental THING of relevance to the enterprise about which data may be kept: things acted on by business activities
people, places, objects, events….
Tangible: customer, product
intangible (active/conceptual): equipment breakdown
look for nouns (beginner) BUT a proper noun is not a good candidate….

22. How to find attributes? Attribute:
property or characteristic of an entity
A descriptor whose values are associated with individual entities of a specific entity type
look for descriptions, characteristics, and properties of entity (beginner)

23. (unique) Identifier
“attributes that uniquely identify entity instances”
Uniquely identify every instance of the entity
One or more of the entity’s attributes
Composite identifiers are identifiers that consist of two or more attributes
Identifiers are represented by underlying the name of the attribute(s)
Employee (employee_ID), student (student_ID) 18