Set up a meeting with a librarian. During your meeting, ask the librarian to describe the situations that come up in the library to which the book checkout system needs to respond. List these external events. Now ask about points in time, or deadlines, that require the system to produce a statement, notice, report, or other output. List these temporal events. Does it seem natural for the librarian to describe the system in this way? Similarly, ask the librarian to describe the things about which the system needs to store information. See whether you can get the librarian to list the important attributes and describe relationships among things. Does it seem natural for the librarian to describe these things? Create either an ERD or a class diagram based on what you learn.