entity-relationship diagram
classes in an adventure game
- named, mobile, place, person, thing, transporter, troll, rover, rock
associations
- owns, at, adjoins, transports_to
exercise
- arrange the classes in an is-a hierarchy
- mark the associations between appropriate classes
- note that a class can be associated with itself
what the ER diagram does not mention
- how associations are implemented: who has pointers to whom
- how state and methods are allocated to classes