Interaction design is design for human use. It involves answering three questions:
One of the important choices for "How do you do"; is between HANDLES and BUTTONS. One choice for "How do you feel?" is McLuhan's "hot" vs "cool". One choice for "How do you know?", is between MAPS and PATHS. Here are two vending machines. One presents a PATH-like interface. One is more like a MAP.
Which do you prefer?
Which is better for the vendor?
Which is faster?
What are the failure and recovery possibilities?

What is a computer? Various metaphors have organized entire careers.

Such powerful metaphors are called "paradigms". They motivate the central questions asked. They help us understand the STYLE of interaction. Understanding competing paradigms helps us understand what various people consider a "good" interaction design.

At least eight distinct phases can be identified in the interaction design process. They range from the concrete instance (path-like) to the general overview (map-like) and from invention to presentation.