1. CS 480: Database Systems
Lecture 5
January 25, 2013

3. Recap Relational Model
Set-oriented Model
Set of Attributes form a relation scheme
Tuples is an assignment of values to each attribute
Set of Tuples form a relation
Set of relations form the relational database.

4. From ER-diagrams to Relational Model
For each (non-dominated, non-specialization) entity set E with attribute set {A1,A2,…,An} we will have a relation scheme E(A1,A2,…,An).
The key of this relation E is the same key of the entity set E.
Book calls non-dominated STRONG

6. Non-dominated Entity Sets:
Passenger(name, address,
phone#,frequent-flyer#)
Flight(number, source,
destination, departure-time,
arrival-time)
Plane(plane-id)
Plane-Model(manufacturer,
number, capacity)
Employee(ss#, name,
address, salary)

7. Non-dominated Entity Sets:
Passenger(name, address,
phone#,frequent-flyer#)
Flight(number, source,
destination, departure-time,
arrival-time)
Plane(plane-id)
Plane-Model(manufacturer,
number, capacity)
Employee(ss#, name,
address, salary)

8. Dominated (Weak) Entity Sets
Let A be a dominated entity set and let B be the dominating entity set.
Let the key of B consist of {b1,b2,…,bn}. Also let A have attributes {a1,a2,…,am}.
Then we will have a relation scheme A(a1,a2,…,am, b1,b2,…,bn).
The key of relation A will consist of any key attributes of the entity set A and all of {b1,b2,…,bn}.
Weak because it doesn’t necessarily have a key on its own.

9. Dominated Entity Sets:
Take-off()

10. Dominated Entity Sets:
Take-off(date)
Will contain all attributes of
Take-off.

11. Dominated Entity Sets:
Take-off(date, number)
Will contain all key
attributes of the dominating
entity set.

12. Dominated Entity Sets:
Take-off(date, number)
Keys will be all the keys of
the dominating entity
(Flight) and keys if any of
the dominated entity
(Take-off).

13. Relationship Sets
Each relationship set R will become a relation scheme R.
The keys of all the participating relationships will be part of the relation scheme R.
Also, any attributes that the entity set R had will be part of the relation R.

14. Relationship Sets:
Reservation()

15. Relationship Sets:
Reservation()

16. Relationship Sets:
Reservation(name, address,
Take-off.date)
All keys of participating
relationships.

17. Relationship Sets:
Reservation(name, address,
Take-off.date)
All keys of participating
relationships.
Are these all the keys
of the participating
entities?

18. Reservation(name, address, Take-off.date, Flight.number)
Relationship Sets:
Reservation(name, address,
Take-off.date, Flight.number)
All keys of participating
relationships.
Look past the diagram
Are these all the keys
of the participating
entities?
It’s missing the
Flight.number, which is
part of the Take-off key.

19. Reservation(name, address, Take-off.date, Flight.number,
Relationship Sets:
Reservation(name, address,
Take-off.date, Flight.number,
date, class, seat#)
All attributes of the
relationship itself.
Look past the diagram

20. From Relationships to Relations
The keys for the relation R will depend on the cardinality constraints.
Many-to-many – All keys of the participating entity sets will form part of the key of the relation R.
One-to-one – Choose the key of either of the participating entity sets as the key for R.
One-to-many – Choose the key of the many side.
Ask why at least for the one-to-one… Also for the one-to-many…

21. Reservation(name, address, Take-off.date, Flight.number,
Relationship Sets:
Reservation(name, address,
Take-off.date, Flight.number,
date, class, seat#)
Take-off-OF-Flight(
Take-off.date, Flight.number)
Take-off-BY-Plane(plane-id,
Plane-TYPE(plane-id,
manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer,
number)
DISCUSS PILOT
WHAT ABOUT N-ary RELATIONSHIPS? All many’s then all keys form part. Some one’s then the keys for all the many’s form part of the key.

22. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-OF-Flight(Take-off.date, Flight.number)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Plane-TYPE(plane-id, manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

23. Weak Entity Sets Don’t have sufficient attributes to form a key.
Dominated Entity Sets (Take-off) and Specialized Entity Sets (Pilot) are examples.
Redundancy will exist if we give a relation to the relationship and the weak entity set.

24. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, Flight.number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-OF-Flight(Take-off.date, Flight.number)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Plane-TYPE(plane-id, manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

25. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-OF-Flight(Take-off.date, Flight.number)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Plane-TYPE(plane-id, manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

26. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Plane-TYPE(plane-id, manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

27. Combination of Schemas
An entity set E in a relationship R has full participation if every element of E participates in at least one relationship in R.
For example:
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Plane-TYPE(plane-id, manufacturer, number)
Every plane has a plane-model, then every plane participates in the TYPE relationship.
Plane and Plane-Type can be combined into one relation Plane(plane-id,manufacturer,number)
This can be done for many-to-one relationships. Combine the “many” relation and the relationship.
Understand WHY it can be done.

28. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, Flight.number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Plane-TYPE(plane-id, manufacturer, number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

29. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id,manufacturer,number)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, Flight.number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)

30. Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id,manufacturer,number)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, Flight.number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)
WHAT ARE THESE? Foreign Keys
What are the implications of them and what’s important about them? Adds a constraint to the database. Referential Integrity… If a passenger changes his name then it should change also on the RESERVATION table…

31. Final Airline Relational Schema
Passenger(name, address, phone#,frequent-flyer#)
Flight(number, source, destination, departure-time, arrival-time)
Plane(plane-id,manufacturer,number)
Plane-Model(manufacturer, number, capacity)
Employee(ss#, name, address, salary)
Take-off(date, Flight.number)
Reservation(name, address,Take-off.date, Flight.number, date, class, seat#)
Take-off-BY-Plane(plane-id, Take-off.date, Flight.number)
Pilot(SS#, flight-hours)
Can-fly(SS#, manufacturer, number)