Protocol – copying objects

When you create shallow copy, you don't duplicate the referred objects that already exists. NSArray's copy method makes shallow copy. If you copy NSArray consisting of 5 NSStrings, only references are copied. Number of NSString object remains five.
When you do deep copy, that makes duplicate of referred object. For above example in deep copy there will be ten NSStrings after the operation.
Depending on need you are free to choose one or mix the operation in your program.

When you create shallow copy, you don't duplicate the referred objects that already exists. NSArray's copy method makes shallow copy. If you copy NSArray consisting of 5 NSStrings, only references are copied. Number of NSString object remains five.