April 2016
Intermediate to advanced
325 pages
9h 24m
English
In reality, the three models are never entirely consistent. For example, the implementation model may be complex and archaic, so you have to simplify what the user sees. This is at odds with the goal of making the implementation model consistent with the UI model.

It’s a trade-off. You are simplifying the user interface so that most users will have a better experience. But this means your UI model may not be entirely consistent with the implementation model.
Let’s say you’re creating an online platform for purchasing downloadable movies. Your potential customers probably know how buying a movie works: