title: what is access_token ,what is purpose of usage or what is it used for?
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/4006695/hows-the-current-state-of-facebooks-session-and-access-token">How&#39;s the current state of Facebook&#39;s session and access_token?</a>  </p>
  </blockquote>
  
  
  
  <p>I am using facebook sdk v3.0 to develop facebook applications. Could you answer following questions for me ; </p>
  
  <p>1) what is access_token ? 
  2) Is it required to store ID of access_token in database with user id ? 
  3) Has access_token specified life time ? </p>