1. COP5725 Database Management ER DIAGRAM AND RELATIONAL DATA MODEL
Prof: Dr. Shu-Ching Chen
TA: Sheng Guan

2. Entity-Relationship Model

3. E- R Data Modeling Example: specific person, company, event, plant
An entity is an object that exists and is distinguishable from other objects.
Example: specific person, company, event, plant
Entities have attributes
Example: people have names and addresses
An entity set is a set of entities of the same type that share the same properties.
Example: set of all persons, companies, trees, holidays

4. Attributes
An entity is represented by a set of attributes, that is descriptive properties possessed by all members of an entity set.
Example:
instructor = (ID, name, street, city, salary ) course= (course_id, title, credits)
Attribute types:
Simple and composite attributes.
Single-valued and multivalued attributes
Derived attributes

5. Relationship Sets
A relationship is an association among several entities
Example: (Peltier) advisor (Einstein) student entity relationship set instructor entity

6. Entity-Relationship Diagrams
Representing entities
we represent an entity by a named rectangle
use a singular noun, or adjective + noun
refer to one instance in naming
CUSTOMER
PART-TIME
EMPLOYEE

7. Entity-Relationship Diagrams
Representing relationship
DEPT
EMPLOYEE
employs

8. Entity-Relationship Diagrams
One to one
One to many

9. Entity-Relationship Diagrams
Many-to-many relationship (M:N): exists when one instance of the first entity can relate to many instances of the second entity, and one instance of the second entity can relate to many instances of the first entity.
(c)
Many to many

10. E-R Diagram for a University

11. The Relational Data Model
Database
Model
(ODL, E/R)
Relational
Schema
Physical
storage
Complex
file organization
and index
structures.
ODL definitions
Diagrams (E/R)
Tables:
row names: attributes
rows: tuples

12. Terminology Attribute names Name Price Category Manufacturer
gizmo $ gadgets GizmoWorks
Power gizmo $ gadgets GizmoWorks
SingleTouch $ photography Canon
MultiTouch $ household Hitachi
tuples

13. More Terminology Every attribute has an atomic type.
Relation Schema: relation name + attribute names + attribute types
Relation instance: a set of tuples. Only one copy of any tuple!
Database Schema: a set of relation schemas.
Database instance: a relation instance for every relation in the schema.

14. name
category
name
price
makes
Company
Product
Stock price
buys
employs
Person
name
ssn
address

15. Entity Sets to Relations
name
category
price
Product
Product:
Name Category Price
gizmo gadgets $19.99

16. Relationships to Relations
Start Year
name
category
name
makes
Company
Product
Stock price
Relation MAKES (watch out for attribute name conflicts)
Product-name Product-Category Company-name Starting-year
gizmo gadgets gizmoWorks

17. Handling Weak Entity Sets
affiliation
Team
University
sport
number
name
Relation TEAM:
Sport Number University-name
mud wrestling Montezuma State U.
- need all the attributes that contribute to the key of Team
- don’t need a separate relation for Affiliation.

18. Relational Data Model Key point: Indicate your primary key
Define attribute’s data type
Indicate the relationship

19. ER Model to Relational Model

20. Populate your relation
Key point:
At least five records are needed for each table.
Also indicate the PK here.

21. Constraint
Key point:
Indicate the constraint at the end