http://www.otierney.net/objective-c.html#inheritance
http://www.google.co.in/#hl=en&q=id+in+objective-c&aq=f&aqi=&aql=&oq=&gs_rfai=&fp=bc4921db69ff5ed7
http://en.wikipedia.org/wiki/Objective-C#Interfaces_and_implementations
http://en.wikipedia.org/wiki/Cocoa_(API)
http://www.google.co.in/#hl=en&q=what+is+ns+in+objective-c&aq=9m&aqi=g8g-m2&aql=&oq=ns+in+&gs_rfai=&fp=bc4921db69ff5ed7
