How do you identify major use cases?

What will be an ideal response?

We arrive at major use cases by analyzing domain concepts marked as "process" or "function". But the conversion ratio is not one-to-one. A use case has features – four required components – that a function or a process may lack. Sometimes we have to break up a process into more than one use case; at other times we might have to combine pieces of multiple processes or functions to arrive at one use case. Other domain concepts, such as objects or business rules, might find their way into use cases if the context requires it.