This was asked here but that was a beta XCode. Now with official xcode 4, I don’t found how to create the Class Model. In XCode 3 this is very easy and obvious: File->New File->Class Model document template in ‘others’.
Anyway, the main question is: There are Class Model in XCode 4?
There is no class model in Xcode 4. The class modeling tool was eliminated in Xcode 4.