EXERCISE SET 3
===============

The exercises are all based on the suppliers-and-parts database:


1. Write a relational algebra expression for each query:

a. Get all pairs of city names such that a supplier in the 
   first city supplies a project in the second city.

b. Get all pairs of part numbers such that some supplier supplies 
   both the indicated parts.

c. Get project names for projects supplied by supplier S1.

d. Get supplier number for suppliers with a status lower than 
   that of supplier S1.


2. Write the integRity constraints for the following "business rules":

a. All red parts must weight less than 50 pounds.

b. Every project must be located in a city in which there is at least
   one supplier.

c. Every London supplier must supply part P2.


3. What is the effect of each of the following operations?

a. UPDATE project J7, setting CITY to New York.

b. UPDATE supplier S5, setting S# to S8, if the applicable referential
   action is RESTRICT.

c. DELETE supplier S3, if the applicable referential action is CASCADE.

d. UDPATE shipment S1-P1-J1, setting S# to S2.