1. Entity-Relationship (E-R) Modeling
Also known as conceptual modeling or semantic modeling
Four Basic Constructs: -Entity -Relationship -Attribute -Cardinality -(participation and connection)
W.E. McCarthy 2002

2. ENTITY: Entities are named objects in the universe of discourse
Types of entities
Thing (truck, building)
Person (customer, employee)
Event
Instant duration (sale, purchase, cash receipt)
Extended duration (month-long use of a truck, a course offering that starts on JAN 3 & ends on 16 FEB)
Concept (category of customer, course)
SYMBOL -- Rectangle
Customer
Course offering
W.E. McCarthy 2002

3. 2. RELATIONSHIP : Association between two (or more ?) entities
Examples:
employee “assigned to” building
customer “participates in” sale
professor “teaches” course-offering
SYMBOL -- Diamond
participates in
Customer
Sale
W.E. McCarthy 2002

4. 3. ATTRIBUTE : Characteristics or elementary properties of entities or relationships. They are used for actual communication about the real world phenomena represented by entities or relationships
Example attributes for the entity INVENTORY:
stock#, color, price, cost, weight
A primary key is a special attribute used to represent an instance of an entity or relationship in a database
Must be unique and universal
Can be a concatenated (combined key)
“No representation without identification”
For this class, we assume that relationships are identified by the keys of their participating entities
SYMBOL – small connected circle (filled in for primary key)
Inventory
Stock# Color Price
W.E. McCarthy 2002

5. 4. Participation CARDINALITY (min, max):
4. Participation CARDINALITY (min, max): These show the correspondence of entities and relationships A
rel B
(min, max)
Entity “A” participates in relationship “rel” at a maximum of
- “1” time (single time only)
- “n” times (many times)
Entity “A” participates in relationship “rel” at a minimum of
- “0” times (optional)
- “1” time (mandatory)
W.E. McCarthy 2002

6. 4. Participation CARDINALITY (min, max): (other side of relationship)B A
rel
(min, max)
Entity “B” participates in relationship “rel” at a maximum of
- “1” time (single time only)
- “n” times (many times)
Entity “B” participates in relationship “rel” at a minimum of
- “0” times (optional)
- “1” time (mandatory)
W.E. McCarthy 2002

7. W.E. McCarthy 2002