1. From E/R Diagrams to Relational Schema
Easier than ODL (using a liberal interpretation of the word “easy”)
- relationships are already independent entities
- only atomic types exist in the E/R model.
Entity sets relations
Relationships relations
Special care for weak entity sets.

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

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

4. 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

5. 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.

6. Modeling Subclass Structure
Product
Platforms
required memory
ageGroup
topic
Educational
Product
Software
Product
Educ-software
Product
Educational-method

7. Option #1: the ODL Approach
4 tables: each object can only belong to a single class
Product(name, price, category, manufacturer)
EducationalProduct( name, price, category, manufacturer, ageGroup,
topic)
SoftwareProduct( name, price, category, manufacturer, platforms,
requiredMemory)
EducationalSoftwareProduct( name, price, category, manufacturer,
ageGroup, topic, platforms,

8. Option #2: the E/R Approach
Product(name, price, category, manufacturer)
EducationalProduct( name, ageGroup, topic)
SoftwareProduct( name, platforms, requiredMemory)
No need for a relation EducationalSoftwareProduct
Unless, it has a specialized attribute:
EducationalSoftwareProduct(name, educational-method)

9. Option #3: The Null Value Approach
Have one table:
Product ( name, price, manufacturer, age-group, topic, platforms,
required-memory, educational-method)
Some values in the table will be NULL, meaning that the attribute
not make sense for the specific product.
How many more meanings will NULL have??