Constraint

Nederlandse vertaling: voorwaarde, beperking, randvoorwaarde, begrenzing, gedwongenheid, restrictie
(Zie bijvoorbeeld Mijnwoordenboek.nl)

Don Norman onderscheidt in “Affordance, Conventions and Design (Part 2)” drie soorten constraints, namelijk fysieke, logische en culturele:

Physical constraints are closely related to real affordances: For example, it is not possible to move the cursor outside the screen: this is a physical constraint. Locking the mouse button when clicking is not desired would be a physical constraint. Restricting the cursor to exist only in screen locations where its position is meaningful is a physical constraint.

Logical constraints use reasoning to determine the alternatives. Thus, if we ask the user to click on five locations and only four are immediately visible, the person knows, logically, that there is one location off the screen. Logical constraints are valuable in guiding behavior. It is how the user knows to scroll down and see the rest of the page. It is how users know when they have finished a task. By making the fundamental design model visible, users can readily (logically) deduce what actions are required. Logical constraints go hand-in-hand with a good conceptual model.

Cultural constraints are conventions shared by a cultural group. The fact that the graphic on the right-hand side of a display is a “scroll bar” and that one should move the cursor to it, hold down a mouse button, and “drag” it downward in order to see objects located below the current visible set (thus causing the image itself to appear to move upwards) is a cultural, learned convention. The choice of action is arbitrary: there is nothing inherent in the devices or design that requires the system to act in this way. The word “arbitrary” does not mean that any random depiction would do equally well: the current choice is an intelligent fit to human cognition, but there are alternative methods that work equally well.

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