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What is Usability?
[1]
- © Q&U
The majority of systems and services which are
provided by computer science, electrical engineering and information
technology, finally address the human user. As a consequence, it is
essential to understand the user and his interaction behaviour for
designing successful systems and services.
Formal
principles for the interface design can be based on this knowledge, as
well as demands on the technical components underlying the system. In
turn, the availability of new technologies may lead to innovative
interface design, and finally to new forms of interaction.
The Three Layers of Usability
The term
“usability” is defined in ISO 9241, Part 11, as “the extent to
which a product can be used by specified users to achieve specified
goals with effectiveness, efficiency and satisfaction in a specified
context of use”. The “Quality and Usability Lab”, which is part
of TU Berlin’s Faculty of Electrical Engineering and Computer
Science, thus tries to address the usability – and in more general
terms the quality – of information and communication technology on
three layers (see picture above):
- the layer of the principles of human perception, judgment and behaviour, which determine the interaction;
- the layer of the design of the interface between user and system; and
- the layer of the fundamental technologies the interaction is based on.
On
all three layers, different media or modalities and combinations of
these may be considered. The most relevant ones for practical
applications are the acoustic, the visual and the tactile interaction.
We address interactions both between human and machine (e.g.
speech-based interfaces, web interfaces, interactions with avatars and
in virtual or augmented environments) and between humans by means of a
technical system (speech and multimedia transmission through wireline
or wireless networks, translation systems, etc.).
Quantifying Quality and Usability
In
order to design high-quality and highly-usable systems and services,
quality and usability has to be measured and analyzed in a consequent
way. Thus, quality and usability are considered to be the result of a
measurement and a prediction process, in which the characteristics of
the system are put into a relationship to the demands of the user. On
the one hand, the performance of the system and its underlying
components has to be measured in a quantitative way. On the other
hand, the user’s perceptions and requirements during the
interaction with the system have to be quantified. The latter may be
accomplished by means of auditory and visual experiments with human
participants. During these experiments, the characteristics of the
systems are usually well defined (e.g. by means of simulations), and
the behaviour and the perceptions of the user are collected and
recorded.
The characteristics of the system can then be
correlated to the user’s perception, and thus design principals can
be derived for the system under investigation. In an ideal case,
quality and usability of a new system or service can already be
predicted in the planning or design phase of system development.
Models which are able to carry out such tasks must quantify quality in
a valid and reliable manner, so that the prediction results correspond
to the judgments of a human user (which is a direct quality
measurement). By combining quality and usability measurement and
prediction, systems and transmission networks can be adjusted to the
user’s requirements in an economic way; this will highly improve the
success and the acceptance of technical systems.
Teaching in Quality and Usability
For
students in electrical engineering, information technology and
computer science, the topic as well as the approach described above
offer the advantage that they learn to estimate the effects of the
systems they develop on the user, and that they get excellently
prepared for interdisciplinary cooperation. Thus, the Quality and
Usability Lab offers courses on all three layers: technology,
interaction-design and user.
Long-term
Goals
Long-term goals of the Quality and
Usability Lab are
- to develop methods of measuring the quality and usability of information and communication technology,
- to put quality and usability into a relationship with the technical characteristics of the systems and services,
- to derive guidelines for system and service design on that basis,
- to predict quality and usability based system characteristics, and
- to implement the described methods in the cycle of specification, planning, design, implementation, optimization and monitoring of new systems and services.
Applications
At the Quality and Usability
Lab, we apply these principles for example to systems for
- transmission of speech, audio and video signals (telephony, Voice-over-IP, radio, IP-based-television, telephone conferences, etc.),
- multimodal human-machine interaction (spoken dialogue systems, web-based services, multimodal dialog systems, etc.),
as well as – in a broader sense – all
systems enabling a multimodal interaction between humans, machines,
and the environment (virtual environments, augmented environments,
context-sensitive systems, etc.).
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