title: iPhone app getting XML then refreshing it at intervals
body: <p>I have an app which gets some data from the web via an XML document. I have this working fine and have followed apples SeismicXML example (uses NSURLRequest etc). I am very new to this so I have to admit that I do not totally understand all the code that gets the XML - but it is working. My problem is that my app may be running for some time so I want to be able to refresh the XML every now and again and check to see if it is different. If it is different I need to update my contents. Basically this means my questions are....</p>
  
  <ol>
  <li>Is there a standard way of doing this? </li>
  <li>I was thinking of creating a timer to call the function which parses the XML but I can't figure out which function to call. </li>
  </ol>
  
  <p>If anyone can give me any pointers or even better examples of this it would be fab. Thanks</p>