Human Interface Principles

Principles are:

• Guidelines to direct our decisions in the design process.
• Derived from assumptions.
• Sometimes contradictory.

Assumptions and principles are interdependent.

Understanding this relationship can guide us in the use of principles to resolve issues in the design process.

1. Direct Manipulation
   • Users should believe they are directly controlling the objects represented by the computer.
   • Physical actions change the physical state of an object.

   Related Assumptions

   • People learn by doing.
   • People feel more comfortable when they are in control.
     

2. Metaphors
   • Familiar models allow people to employ knowledge they have already learned in another context.
   • Use models from the real world.

   Related Assumptions

   • People learn no more than they need to get the job done.
     

3. Work Flow
   • The computer should not interrupt the user's train of thought; it should be transparent.
   • Users should not be forced to change their focus.
   • Provide multiple paths to complete a task.

   Related Assumptions

   • People learn no more than they need to get the job done.
   • People can remember seven plus or minus two items at a time.
     

4. Consistency
   • Provide similar ways of operating in similar contexts.
   • Promotes transfer of skill.
   • Allows users to focus on new and different areas.

   Related Assumptions

   • People learn no more than they need to get the job done.
   • People learn in chunks that with use are integrated into a whole.
     

5. Simplicity
   • Keep the graphics of the display simple.
   • Keep the language of the interface simple; i.e., the number of objects and rules.
   • Present tasks in small learnable chunks.

   Related Assumptions

   • People can remember seven plus or minus two items at a time.
   • People learn in chunks that with use are integrated into a whole.
   • People learn and communicate in different ways.
     

6. See and Point
   • Make all available options readily accessible to the user.
   • Don't force the user to remember what to do.
   • Provide "Aha!" triggers on the screen.

   Related Assumptions

   • People are better at recognition than recall.
   • People feel more comfortable when they are in control.
     

7. Feedback and Communication
   • Provide immediate feedback.
   • Always keep the user informed.
   • Communications should be brief, direct, and expressed in the user's vocabulary.

   Related Assumptions

   • People learn by doing.
     

8. Forgiveness
   • Expect mistakes.
   • Actions should be reversible.
   • If actions are not reversible, then let the user know.

   Related Assumptions

   • People learn by doing.
     

9. Perceived Stability
   • No arbitrary changes; size and position of elements remain stable.
   • The screen accurately reflects the state of the world.
   • Instability is disorienting and error-prone.

   Related Assumptions

   • People feel more comfortable when they are in control.
     

10. Visual Communication
    • Visually confusing displays detract from the effectiveness of the interface.
    • Provide clues for users.
    • Match the graphic and behavior.

    Related Assumptions

    • People learn and communicate in different ways.
      

Some caveats

Some principles conflict with others.

A good interface is likely to violate some principles.

The corollary of this is before breaking with these principles, you should understand why the principle exists, why following the principle will weaken your interface, and why breaking the principle will improve your interface.

Reversing the relationship

So far, we've talked about principles, and related them back to assumptions. What principles do each of the assumptions support?

1. Assumption: People learn by doing.

   Principles:

   • Direct Manipulation
   • Feedback and Communication
   • Forgiveness

2. Assumption: People feel more comfortable when they are in control.

   Principles:

   • Direct Manipulation
   • See and Point
   • Perceived Stability

3. Assumption: People are better at recognition than recall.

   Principles:

   • See and Point

4. Assumption: People learn no more than they need to "get the job done."

   Principles:

   • Metaphors
   • Work Flow
   • Consistency

5. Assumption: People can remember seven plus or minus two items at a time.

   Principles:

   • Work Flow
   • Simplicity

6. Assumption: People learn in chunks that with use are integrated into a whole.

   Principles:

   • Consistency
   • Simplicity

7. Assumption: Different people learn and communicate in different ways.

   Principles:

   • Simplicity
   • Visual Communication

Is the mapping between assumptions and principles complete? Of course not.