CS 4604 Homework #1

1. (8 points) It is possible for a many-one relationship to be symmetric. Carefully state the conditions under which this can happen.
   
   
2. (10 points) Readup Chapter 4 upto and including Section 4.2.8 of your textbook and answer Exercise 4.2.6. After completing parts (a)-(c), perform the following additional modification without introducing any new classes:
   
   (d) Each ship assigned to a task group is given a priority (for that task group). The ship with the highest priority is always given a 1 (for that task group) and the numbers increase in steps of 1. Ships may thus get different priorities for different task groups they are part of. But the ships do not conversely assign any priority for the task groups they are part of (they don't care!).
   
   For full credit, include the final ODL code containing all four modifications.
   
   
3. (12 points) Express the E/R diagram of Fig. 2.7 in ODL.
   
   
4. (20 points; From the Spring 2000 Final) Design an E/R diagram for the following situation: Doctors prescribe drugs for patients. A given doctor can prescribe many drugs for a certain patient. A patient may be treated by many doctors and can be prescribed the same drug by different doctors. Drugs can only be purchased by presenting prescriptions to the pharmacist. A prescription can involve more than one patient (e.g., a mother and her baby), more than one drug, but is associated with a unique doctor. If there are parts of the problem that cannot be modeled, state these in the margin of your diagram (as "Notes").