On 15.09.2011 11:39, Samnang Chhun wrote:
> I would like to learn how to build a background running program that
> track all questions of ruby related questions on Stack Overflow
> http://api.stackoverflow.com/1.1/questions?tagged=ruby and alert to me
> somehow.
>
> But the question is how do I know when new questions has asked on Stack
> Overflow and get only those?

You fetch it regularely (but don't abuse the service) and diff what has 
changed; you could use the "creation_date", "last_edit_date" or 
"last_activity_date" to figure out which ones you want to see.

HTH