ERD Constraints. Am I on the right track or barking up wrong tree?

I'll put what I understand by "optionality" in OO terms:

[This Thing] 0..1 -------- 1..* [That Thing]

Look at [This Thing]. The 0 says that the association is optional. ie. You can have an Object or not. If you do, then that Object can have this particular kind of association or not.

Now [That Thing]. If you have such an object, then you must have one of these associations.

ie. the notation refers to the optionality of the Association, and not of the Object, but a side effect of the 1..* (or 1..1) rule of association is that the Object becomes not-optional.

Am I right? Or am I on completely the wrong track? This feels to me like a bit of insight, but many's the time when "insight" is none other than completely losing the plot.

They explain it in Chapter 9. You have got the right idea, yes.

Thanks. I didn't feel like I was completely getting it, reading Ch 9. When one switches from active to passive voice, and back again, you obviously change the focus from one object to the other, and this tends to shortcircuit me.