1. Errors in ER Diagram
Do not represent a concept as both a relationship type and an attribute
Make sure every entity type must have a key attribute
Relationship type connects 2 entity types (In general, cannot connect a relationship to another entity type; There is an extension which allows it (see fig. 8.11)
Avoid chain of composite attributes
Don’t forget to include role names for recursive relationships

2. Online Bookstore

3. Roles missing!!
Every entity type must have a key
Should publisher be an entity type?
Can a product have multiple prices?

4. Key attribute for author is missing
Customers??
Can a book have multiple prices?

5. Author has no key attribute
Can’t tell what’s the price of the book purchased by user; not sure what payment method is used

6. Should author be an entity type?

7. Diagram is disconnected
Not all concepts need to be modelled ?

8. Not sure what this relationship type is

9. Crime Database

10. Key attribute missing for crime instance
Should officer be an entity type?
Does the database store only offenders who have been proven guilty of committing the crime; what about criminal suspects?

11. You cannot relate an entity type to a relationship type via another relationship type.
Every entity type must have a key

12. Roles missing!
Every entity type must have a key
Use of “Identifies” as key is wrong
Try to avoid chain of composite attributes

13. Key attribute for punishment is missing
Case officer?

14. Flight Reservation

15. Draw the rectangles!
Avoid chains of composite attributes!

16. Passenger/Reservation?
Departure vs arrival airport?
Solution is in the textbook (exercise section)

17. Need to distinguish between scheduled and actual arrival/departure information
Flights should not be a multivalued attribute of airport
What is the difference between destination of flight and arrival airport?

18. Electronic Medical Records

19. Medications could be made into an entity type
Physicians?
See example from homework 1

20. Online Photo Sharing

21. Username is not a composite attribute
Username is not a composite attribute!! password should not be a component of the composite attribute.

22. College Football/Basketball

23. You can't have both relationship type and entity type called teams/coaches/players
Every entity type must have a key
Name of entity type should be singular
Does college player have salary?

24. Results for different games played by a team are not available (only #wins and #losses)

25. Where do the stats derived from?
Cannot draw a line from one entity type to another without a relationship type

26. Every entity type must have a key
Cannot tell which player plays in a game

27. Every entity type must have a key
Can a coach coach a team but not a player who plays for the team?
Can a coach coach a player who does not play for the team coached by the coach?