From: Peter.Gorny@arbi.informatik.uni-oldenburg.de (Peter Gorny)
Subject: Re: cost of poor usability metrics
Organization: University of Oldenburg, Germany
Date: Thu, 9 Apr 1992 11:02:42 GMT
Keywords: usability use efficiency

bobd@zaphod.UUCP (Bob Dalgleish) writes:

>I disagree that a software-based product consists mostly of "features".
>All programs consist of a foundation, functions that use that foundation
>to manipulate data, and features which are compositions of functions
>applied in various ways.


Accepted. But consider, that all has to fulfill the user's task within
the user(s)' capabilities.

We use another taxonomy here, developed in the context of "MUSE" (Method 
for USer Interface Engineering).
A preposition is the list of application fucntions which the user needs.
In the first step these functions (and the objects they work on) are
investigated in regard to possible priorities when solving specific parts
of the task, by groups of users with specific system knowledge and task
knowledge, including descriptions of usage (frequency, regularity,
intensity of use). Another important investigation has to find similarities
of objects and functions (so the designer can design a "consistent" usage
surface for the construction of the user interface.
From these findings you can derive necessary "control functions" (resulting
solely from the fact, that you are using the computer as a tool/medium and
not another device, e.g. pencil&paper) and "adapting functions", so the
user can adapt the surface to his/her habits, taste or specific tasks.
Finally we have to define a set of "metafunctions", allowing the dialog
about the dialog; the normal help function are placed here - but new systems
include a variety of (often knowledge based) support here. The fault handling
(user's slips, faults, errors, mistakes...) necessitates a metadialog in most
cases.
 
All four types of functions can be mapped onto a set of "abstract" dialog
forms: command input, data input, multiple choice and direct manipulation 
of (displayed) objects.
These four types again can be combined (eg. several data inputs to form 
filling -> "mask") and realized in a variety of techniques: the multiple 
choice, for example, as a menu, a list of commands, function keys, a palette 
of icons  etc.

I did not forget your point - the short description of MUSE above is meant 
as an introduction to the opposite approach to designing a usage surface -- 
evaluating existing ones, but with the same principled approach.

It offers no metrics directly, but it shows that -- if you want to use 
metrics -- you have to find different ones for the different parts of evalu-
ation. And each will not give you more than some hints about that specific
part, with all the range of errors always included in psychological experiments.

Peter Gorny



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Xref: sparky comp.human-factors:1166 comp.cog-eng:200