"When it comes to subclassing, knowing which methods are ‘primitive’ methods is important.
The notion of primitive methods are those methods form the basis of the public interface/class.
The rest of the methods are just convenience methods built around them. When overriding a
class behavior with subclassing, just overriding those primitive are often enough." Ref[1]
Reference
1. Learning Objective-C -– Primitive Methods
https://ktatsiu.wordpress.com/2010/05/16/tips-of-learning-cocoa-for-a-c-programmer/
2. What are the 'primitive' accessors for in Core Data?
http://stackoverflow.com/questions/7427373/what-are-the-primitive-accessors-for-in-core-data
3. Programming with Objective-C
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html#//apple_ref/doc/uid/TP40011210-CH1-SW1
4. A quick reference cheat sheet for common, high level topics in Objective-C (AAAA+)
https://github.com/DiamondStudio/Objective-C-CheatSheet