July 19, 2008


In this post I briefly discuss usability. First of all, I have to say that there is so much research that it is nearly impossible to write a short blog post about this topic. For instance, Jakob Nielsen, a popular usability expert, writes about usability for years. So I will just give you a quick impression by introducing the GOMS approach, which I found very straightforward and easy to apply. I especially use it to evaluate the task performance of my approach to diagram completion.

GOMS is an acronym for Goals, Operators, Methods, and Selection rules. The approach, however, is much easier than these terms suggest. The key idea is, that you write down all operations that have to be performed in order to achieve a given goal. Depending on its kind a predetermined execution time is attached to each of these operations. For instance, a keystroke takes 0.28 seconds for an average user, pointing with the mouse to an object on the screen lasts round about 1.1 seconds. There are several more kinds of actions and appropriate average times (determined on an empirical base). Summing up the times for all necessary operations finally yields the task execution time. Once you have this time you can compare different user interfaces, you can evaluate changes to the user interface and so on. It's that easy.

Note that in the context of the Visual Week (15.-21.09.08 in Herrsching am Ammersee, Germany) there will be a tutorial on another popular usability approach called Cognitive Dimensions. Here, usability is evaluated on a much higher level. To quote from the tutorial website (accessed 19 July 2008):
The Cognitive Dimensions of Notations (CDs) framework is the world's leading approach to understanding the usability of programming tools. It provides an analytic framework and design vocabulary that can be used to evaluate and improve, not only programming languages, but a wide variety of environments and notations for design, problem-solving, and creative work.

Currently I apply usability evaluation methods to my approach on diagram completion. In my talk "Exploiting the Layout Engine to Assess Diagram Completions" to be held at the layout workshop LED 2008 (satellite event of VL/HCC 2008) I will present a first improvement: in certain situations a special shortcut can more than double the task performance (to speak in terms of GOMS). Stay tuned!

Further reading:

  • Stuart Card, Thomas P. Moran and Allen Newell: The Psychology of Human Computer Interaction. 1983.

  • GOMS Model Work, comprehensive website about GOMS maintained by David E. Kieras.

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