How to selete the best answer?

Thanks, but there should be some rules about the Rating features.

- what's the time limitation for rating?

- after a "best answer" rated, is other answer can instead of the previous one?

Thanks for your best explanation,

But I am afraid the concept hard to work without a strong search engine deliverory. 

Yedda is just a "kowledge Community", but Knowledges need a Search Engine a "Knowldge Search"

In fact, I setup a Knowledge Search channel in Jan 2006, and operated it more than 4 months.  I have some thoughts about this business.

Yedda has so much creative features, and Yedda is the best Tagging-Knowledge Community I have ever seen.

In my thought, a Knowledge Community is very hard to meet success,  a Key problem is how to deliver questions and knowledge to world wide users. A in-house tag browsing feature is not enough.