Chapter 2: Implementation Models and Mental Models

How the machine or program works is the system model (Donald Norman), or as the authors of the book call it, the implementation model.

Users don't know complex details of how something works - they create a "cognitive shorthand" for it, known as a mental model or conceptual model.

What designers come up with to communicate a user's mental model to the implementation model is the designer's model (Donald Norman), or represented model. The goal of a designer should be to relate their model with the user's mental model.