grammar : "of", " 's" or nothing ?

[Yoann Le Bleis]

Does anyone have a good link to a page that exhaustively defines the use of
*of*,  *'s* and *nothing* in a nominal group?
I learned these rules a few years ago, but I cannot remember them exactly...

Can I use the *'s* for an object possessing another object? eg "widget's
event"
What about concepts?
How can I choose between "confidentiality rules" and "rules of
confidentiality"?

I hope my request is clear enough...

Yoann
French intern in tech. doc.