A university library database records information about books; for each book, it records the book isbn number

(which is unique), and the book name. In addition, it records which books have been checked out : the

information it keeps for the books which have been checked out is the student id of the student who checked it

out, and the date on which the book was checked out. Some books may not be checked out. You can assume

that there is only one copy of each book.

Each of the following situations concerns how we capture the information in dierent situations.

Situation 1:

For each book, we only keep track of the student who has currently checked out the book i.e. we don't keep

track of who checked out the book in the past.

Situation 2:

For each book, we keep track of the student who has currently checked out the book and we also keep track

of who checked out the book in the past. Here you can assume that no student ever checks out the same

book more than once.

Situation 3:

For each book, we keep track of the student who has currently checked out the book and we also keep track

of who checked out the book in the past. Here it is possible that the same student has checked out the

same book more than once; for example, once on June 4, 2013 and another time on July 19, 2013. You can

assume that no student can check out the same book twice on the same day.