In programming, the methods of a class can be placed into the following three categories:

Data TransformationEdit
A method whose responsibilities is to transform a set of data received as input into a set of data that will serve as input to something else.
Simple Example: Encrypt method of a MD5Encryption class. CheckOut() Method on a Cart class.
A method whose responsibilities is to sequence call to one or more dependencies (classes) based on conditions in order to accomplish a certain task.
Simple Example: ExecuteLogin method on a Login class that determines which AuthenticationProvider to use and then calls it depending on the type of user that is logging in.
External communicationsEdit
A method whose responsibilities is to perform actions on another system.
Simple Example: ExecuteNonQuery() method of the SqlCommand class in .Net. Or the ReadFile() method of the File class.
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