I tried to log on to Oracle following the directions in the or-intro
document, but I got a weird response.
What did I do wrong?
Answer: Patience, Patience! We'll get you all accounts on Oracle at the appropriate time. That's what the on-line regstration is for, so don't forget to sign up soon, if you haven't done so already. You'll also get an email to the cs145-all list when the accounts are ready.
A can't think of a real-world example that matches the requirements
of the problem.
Answer: Actually, it's better to think of it as an abstract problem, with no interpretation on the entity sets A, B, and C, and no meaning for the entities used in your example.
What does representative mean?
Answer: It means the same thing as component in lecture notes 2, when talking about "Different Subclass Viewpoints".
Can I have a hint for this question?
Answer: Yes you may. It is pretty near to impossible to count the number of possible subsets of the entity sets that form a tree at the root for n > 2. Notice that these sets are any that (a) include the root, and (b) if they include a node also include its parent. However, if you think about it, you can write a simple recurrence that gives f(n) (the number of subsets for n) in terms of f(n-1). This recurrence cannot easily be expressed in closed form (at least I couldn't do it), but it enables you to answer the question up to 5.