Appropriateness asks whether the functions help the user complete the task in the intended context. A measure relates successful task completion to the functions provided. A product can be complete and correct and still be inappropriate: the functions exist, they work, and they do not fit the way the task is done. This family is the bridge between the product and the context of use, and it needs a task, a user group and a setting. That makes it the most expensive of the three functional families to measure and the one most often skipped. The measure should be built from observed task completion, not from a feature review.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.