I've been trying to figure this out for a while. Let's say you have a person, for example. An attribute of a person is his or her social security number, right? But a person also
has a social security number. So, in an ER diagram, you could draw a square box for
person and a square box for
ssid, and you could connect them by a diamond,
has. Alternatively, you could draw a circle,
ssid, and you could connect it to a square
This isn't just true of
ssid, though. It's possible to draw either-or with concrete things, like a car, a pet, or a phone number, or with conceptual things, like a phone number, a friendship, or a mood. So, where do I draw the lines? Is the object of design just to get everything down on paper and looking nice, or should I be using a guide?