Use the E-R approach to model the operations of your local community library. The library has books, CDs, tapes, and so forth, which are lent to library patrons. The latter have accounts, addresses, and so forth. If a loaned item is overdue, it accumulates penalty. However, some patrons are minors, so they must have sponsoring patrons who are responsible for paying penalties (or replacing a book in case of a loss).