Summary level	User-goal level	Sub-function level
borrow library books (User)
	check-out books (User)
	check status of book loans (User)
	check availability of book (User)
	put hold on book (User)
	recall books* (Department/University)
	return books** (Returner)
	report lost book** (Librarian)
		identify user (User)
		register book (User)
		search for book (User)
		return book (Returner)

* A special use case because it is time-triggered and it is used to enforce borrowing rules (a concern of the university)

** not mentioned in problem statement