My problem is about the possessive s (the ownership s) not that ending-s.
For example, we say, America's Flag, here the America has gotten one ownership s that is America is the owner of that Flag. And also we say, Computer Science, here that Computer doesn't get the ownership s (why?) even though we talk about Science which is of Computer (here).
My question is when we should add that s to the end of the first name which appear to be the owner of the second name? Or how we can recognize what names get that s, please?