Being a relative newbie at doing data modelling, I would like to have some suggestions for doing a ERD for the following situation:

A company is openned with a number of shares.
Each share has a distinctive share number.
Shares can be offered to the public through a Public Share Offer.
Shareholders can take up shares marketed by Brokers.
Brokers earn commission on investments procured.
Shareholders can resell or transfer the shares they've taken up to other or new shareholders.

I've created a basic model, but am unsure of quite a couple of aspects. Anyone with some familiarity with these kind of DB's advice will be appreciated. If you know of good sources of ERD examples for different kind of businesses, please let me know.

Thanks a million,