CS 317: Assignment #2

"Designing E/R Data Models"

General Info

Out: Thursday, April 11th, 2002

Due: Thursday, April 18th, 2002

Changed: 4/16/2002

In this assignment you will be expressing assumptions in E/R data models and distinguishing relationships using keys.

Assignment History

Assignment Checklist

Part 1: Babies, mothers, nurses, and doctors

Do either exercise 2.2.5 or 2.2.6 from Ullman and Widom. (In the First Edition, these are exercises 2.3.2 and 2.3.3.)

Part 2: Keys for relationships

Do exercise 2.3.2 from Ullman and Widom. (In the First Edition, this is exercise 2.5.3.)

It may be helpful to think about particular relationships for each of the four subparts. (You can look through your notes for the examples we've discussed in class.) For example: for "many-many", we could imagine a relationship linking my friends to the foods that they like. We could represent this relationship as a table like below:

Likes:    friend | food
           John  |  pizza
           Mary  |  french toast
           Bill  |  pizza
           Bill  |  french toast

The idea of a key for a relationship is that you want to uniquely identify a particular row in the table. Your task is made more complicated because you are dealing with entities (which have their own keys), but the basic idea holds.