1. Attributes and Domains
Nonkey Attributes
Attribute Definition
Identifying Attributes
Attribute Considerations
Derived Attributes
Multi-valued Attributes
Time-Dependent Attribute Values
Space-Dependent Attribute Values
Attribute Data Types
Attribute Domain Business Rules

2. Non-key Attributes (cont.)
Four major issues with non-key attributes
Identifying descriptive attributes
Placing attributes in the correct entity
Rules of normalization
Appropriate functional dependency
Fixing problem attributes
Identifying the appropriate data type for the attribute (field)
Specifying appropriate domain business rules for the attribute (field)
Later
Later
Later
Later

3. Each student name one attribute for the ___________________ entity
Attributes Exercise #1
Each student name one attribute for the ___________________ entity
Name five ‘aspects’ or ‘characteristics’ that are observably true about occurrences of this entity but that the organization would not wish to record in the DB (or that would be illegal to record)

4. Identify all attributes for five entities in our data model
Attributes Exercise #2
Identify all attributes for five entities in our data model
Are any of them—
Multi-valued
Time-dependent
Space-dependent
Time and space-dependent
Derivable

5. Describing Attributes
Attributes must be described just like entities
What do these mean for a Product entity?
Price − Weight
Supplier − ProductID
“Street address excluding apartment number or P.O. Box where employee receives mail”
“Shipping weight of one unit of product including packaging in decimal fractions of a pound”
“Current retail price that will be charged to a customer purchasing this product”
Use Attribute description in SQL table definitions

6. Describing Attributes Exercises
Are there any attributes whose names are ambiguous?
Write attribute descriptions for several attributes
Choose some ‘obvious ones’ like address

7. Entities and Attributes
There can be ambiguity—depending on perspective—in determining what should be an entity and what should be an attribute
UCF may have an attribute of STUDENT that contains the high school each student graduated from
The State of Florida Dept. of Education may consider high schools to be an entity with its own attributes
Refinement of the database may require that some attributes be turned into new entities—watch for this as we continue in the course

8. Derived Attributes
Meets our definition of an attribute (information we wish to record about an entity)
Value can be derived or calculated from other data in the DB
Same entity
Multiple entities
Student.GPA
Employee.YearsOfService
Employee.Age

9. Derived Attribute Exercise
For each derived attribute discovered in the list:
Identify how each record’s attribute value could be calculated
Identify the pros and cons of explicitly storing a value for this derivable attribute
Recommend whether or not the value should be explicitly stored

10. Multivalued Attributes (cont.)
Remove multivalued attributes by creating a new entity
PK of new entity is often the PK of the original entity plus the formerly multivalued attribute

11. Multivalued Attribute Exercise
Select some multivalued attributes found in the entities
and fix them
How is the MV attribute problem similar to the
M:M Relationship problem?

12. Time Dependent Data
Sometimes the values of attributes are dependent on time
Graduation requirements are dependent on catalog year
Product prices will vary over time
Organization may require access to historical values, not just current values
A new record must be created for each time dependent value

13. Time Dependent Data (cont.)
Create a new entity
Consider original PK and StartTime or StartDate as composite PK
Add attribute of interest as nonkey attribute Consider EndDate/EndTime as nonkey attribute that can be nullable
Consider retaining current value of attribute in the original entity for performance purposes

14. Time-Dependent Attribute Exercise
Fix attributes whose values vary with time
when maintaining historical values is important
Can you write the SQL to determine the price of a rental video on a specified date?

15. Time Dependent Data (cont.)
Similar problems may exist for spatially dependent data
Anybody remember “Prices slightly higher west of the Mississippi”?
Start times for television programs
Prices
Sales tax rates
What do we do if attribute values vary by space and time?

16. Location-Dependent Attribute Exercise
Fix attributes whose values vary with location
Fix attributes whose values vary with both location and time

17. Attribute Data Type Exercise
Specify the data type for each attribute for some selected entities
Support your decision
Q: How does attribute data type selection affect our design goals?

18. Attribute Domain Business Rules Exercise
Identify some attributes for which values legal under the attribute’s data type would not make business sense
Specify business rules about these attribute values