Objects are the root of the Objective-C family tree. Methods Methods are the operations that Objective-C applies to data. Messages Messages are the way one instance of a method requests another method to perform and operation. Classes Classses are how objects are defined. Classes contain the prototype object variables and methods.
Classes inherit variables and methods from a higher level class called a super-class.
A class that inherits some or all of the methods and variables is a sub-class. Categories Categories are ways to declare Methods that can be implemented by any class. Remote Messages Remote Messages support the distribution of objects into different threads of execution and across different computers. Remote Messages are the heart of distributed application progressing. Multi-tiered distributed applications are one of the hallmark features of the OpenStep architecture.