guidelines towards usability (DG) instantiated to the
particular domain of AAI. First, key features included
in the most well known AAIs are identified. Taking
as starting point the most solid factors proposed by
the Usability Engineering approach (Mayhew, 1999),
general mechanisms are added to every feature, thus
providing a set of minimal DG for developing usable
AAS. Some questions are added to every DG in or-
der to clarify its intended meaning in this particular
domain. Furthermore, on the basis of the comparison
between the proposed recommendations and the most
classical usability related questions (e.g. those ques-
tions which help to concretize every general UPs),
traditional usability principles are linked to measure
quality in use of everyDG. Our final goal is to help the
design, development and evaluation of usable AAS.
2 ARGUMENT ASSISTANT
SYSTEMS
Argument assistant systems (AAS) (Verheij, 2003;
Van den Braak et al., 2006) have evolved as software
tools which provide an aid for drafting and generat-
ing arguments, assisting the user in his reasoning pro-
cess. This assistance involves several aspects of the
argumentation process (e.g. keeping track of the is-
sues that havebeen raised, assumptions that have been
made, evaluating the justification status of the state-
ments involved in the argumentation process, etc.).
More specifically (Verheij, 2003), AAS are aids to
drafting and generating arguments by a) administer-
ing and supervising the argument process, b) keep-
ing track of the issues that are raised and the assump-
tions that are made, c) keeping track of the reasons
that have been adduced for and against a conclusion,
d) evaluating the justification status of the statements
made, and d) checking whether the users of the sys-
tem obey the pertaining rules of argument.
Most AAS provide different kinds of facilities to
support argument diagramming, resulting in “box and
arrow” diagrams and allowing to formulate premises
and conclusions as statements. These are represented
by nodes which can be connected by lines to display
inferences; arrows in such lines indicate the inference
direction. Some AAS provide facilities for displaying
a text file in natural language, from which arguments
are to be extracted and analyzed. Several AAS cur-
rently exist (Kirschner et al., 2003), among which we
can mention Araucaria (Reed and Rowe, 2004), Ar-
guMed (Verheij, 2003), Compendium (Okada et al.,
2008), and AVERs (Van den Braak et al., 2006).
In spite of their differences (e.g. the intended
application domain), some common features can
be observed in most AAS interfaces (AAI). First,
they convey the representation of some user men-
tal model (i.e., all the cultural and personal-biased
users’ perceptions and assumptions, as well as their
pre-conceptions about how the system is expected
to react), together with the interaction style (i.e., all
the ways the user can communicate or interact with
the software, including both physical and mental ac-
tions). Additionally, AAS offer feedback and sup-
port for the user (related to explicitate the current
system status, helping the user to prevent, recognize,
diagnose, and recover from errors and misuse, e.g.
by means of help and documentation, undo options,
etc.) as well as diverse interoperability facilities (such
as links to multimedia elements). In many cases,
there are also collaborative features associated with
AAS (such as different kinds of awareness, the syn-
chronization, the visualization of shared workspaces,
the communicationmechanisms, the representation of
self and other’s performance and profiles, the shared
knowledge , etc.). On the other hand, there are some
common features in AAS interfaces typically associ-
ated with the argumentation process itself. Two cen-
tral features are the visual argument representation
(including the recognition of different types of argu-
ments, their statuses, etc.) and the modeling of con-
flict among arguments which allows the user to recog-
nize the argumentation situation under consideration,
Another feature is the preference criteria associated
with the possibility of visualizing or deducing how
the conflict among arguments are resolved.
3 USABILITY PRINCIPLES
Usability is formally defined by ISO 9241-11 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”.where the context of use is a description of the
actual conditions under which the interactive system
is being assessed, or will be used in a normal work-
ing situation. Usability Engineering is a systematic
approach to improving the usability of user interfaces
by applying a set of proven methods throughout the
system development lifecycle.
Usability is such a complex concept that has been
divided in a series of measurable principles (also de-
noted usability attributes) in order to be understood in
a better way. Alternative sets of UPs have been pro-
posed, each of them emphasizing different features
present in usability definition. Also diverse classifica-
tions are proposed when linking them with the formal
definition. In spite of this situation, nowadays some
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