think-cell technical report TC2003/01 A GUI-based Interaction ...

4.2 Interaction Toolbox INTERACTION CONCEPT
4.2.1 Usability Metrics and Design Objectives
In an attempt to understand the very general concept of usability, I suggest the
definition from ISO 9241 as found in [DFAB98]:
“By usability we mean the effectiveness, efficiency and satisfaction with
which specified users achieve specified goals in particular environments.”
Effectiveness. “The accuracy and completeness with which specified users can
achieve specified goals in particular environments.”
For example, a fork is not effective to eat soup with. Effectiveness comes
before efficiency: If a goal cannot be achieved at all, it can certainly not
be achieved with any reasonable amount of resources. On the other hand,
although I have doubts about its efficiency, Microsoft PowerPoint is definitely
effective for the creation of slides. This is proven by the sheer amount of
PowerPoint presentations that have been created to date.
Efficiency. “The resources expended in relation to the accuracy and completeness
of goals achieved.”
For example, I claim that PowerPoint is inefficient if perfectly aligned layout
is the goal, because the pixel-oriented layout specification can be either fast
or accurate, but hardly both at the same time.
Satisfaction. “The comfort and acceptability of the work system to its users and
other people affected by its use.”
It is certainly desirable that the use of software does not adversely affect
people’s health and it is also proven that constant dissatisfaction has negative
impact on productivity and creativity. Therefore, it’s the developers’ job to
create software that is not only highly effective and efficient, but also makes
the user feel in good hands and pleases her from an aesthetic point of view.
Effectiveness, efficiency and satisfaction set the goals for a usable interface; how-
ever, these terms do not say anything about how the goals can be reached. There
are a myriad of terms, methods and rules that describe the characteristics of “good
usability”. The following design objectives subsume some of the most important
aspects of usable software (again, quoted from [DFAB98]).
Learnability. “The ease with which new users can begin effective interaction and
achieve maximal performance.”
For the present work, this objective requests that skilled PowerPoint users
should be able to use the smart grid with little training or instruction. To
achieve this, all the functionality already known from plain PowerPoint must
behave exactly the same with or without the add-in. The behavior of any ad-
ditional UI components should be modelled after the example of the existing
PowerPoint user interface, but it might be helpful to make new features visu-
ally distinctive from the original PowerPoint, so that the user can easily tell
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