Norman’s Gulfs of Execution and Evaluation

“The basic idea is simple.  To get something done, you have to start with some notion of what is wanted—the goal that is to be achieved.  Then, you have to do something to the world, that is, take action to move yourself or manipulate someone or something.  Finally, you check to see that your goal was made.  So there are four different things to consider: the goal, what is done to the world, the world itself, and the check of the world.  The action itself has two major aspects: doing something and checking.  Call these execution and evaluation.”  [Norman, p. 46.]

The Seven Stages of Action

1    Forming the Goal

Something to be achieved.  Can be stated in a very imprecise way, e.g., “make a nice meal”.

Execution

Norman's Stages of Execution

2    Forming the Intention

Goals must be transformed into intentions, i.e.,  specific statements of what has to be done to satisfy the goal.  E.g., “Make a chicken casserole using a can of prepared sauce.”

3    Specifying an Action Sequence

What is to be done to the World.  The precise sequence of operators that must be performed to effect the intention.  E.g., “Defrost frozen chicken, open can, …”

4    Executing an Action

Actually doing something.  Putting the action sequence into effect on the world.  E.g., actually opening the can.

Evaluation

Norman's stages of evaluation

5    Perceiving the State of the World

Perceiving what has actually happened.  E.g., the experience of smell, taste and look of the the prepared meal.

6    Interpreting the State of the World

Trying to make sense of the perceptions available.  E.g., Putting those perceptions together to present the sensory experience of a chicken casserole.

7    Evaluating the Outcome

Comparing what happened with what was wanted.  E.g., did the chicken casserole match up to the requirement of ‘a nice meal’?

Both Gulfs as a Single Diagram

Norman's Seven Stages of Action

Practical Application

Design Questions

The seven stages of action prompt the following design questions: [Norman, p. 53]

How easily can one:

  1. determine the function of the device?
  2. tell what actions are possible?
  3. determine mapping from intention to physical movement?
  4. perform the action?
  5. tell  what state the system is in?
  6. tell if system is in desired state?
  7. determine mapping from system state to interpretation?

Principles of Good Design

The significance of these questions can be summed up as the following principles of good design:

  • Visibility.  By looking, the user can tell the state of the device and the alternatives for action.
  • A good conceptual model.  The designer provides a good conceptual model for the user, with consistency in the presentation of operations and results and a coherent, consistent system image.
  • Good mappings.  It is possible to determine the relationship between actions and results, between the controls and their effects, and between the system state and what is visible.
  • Feedback.  The user receives full and continuous feedback about the results of actions.  [Norman, p. 53]

Reference: http://www.it.bton.ac.uk/staff/rng/teaching/notes/normangulfs.html

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