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Unformatted text preview: the user’s head, substitutivity can control user errors and cognitive effort (Dix et al.,
Customizability is the ability of modification of the user interface by the user or the
system. This ability concerned with the automatic modification that the system would
make based on user knowledge. It is important to distinguish the difference between the
user-initiated and system-initiated modifications, associated with the former as
adaptability and the later as adaptively (Dix et al., 1993).
Adaptability associates to the user’s ability to adjust the input into output. This
customization may be very limited, that the user just allowed adjusting the position of
soft buttons on the screen, or redefining command names. Adaptively is the automatic
customization of the user interface by the system however decisions for adaptation
could be based on user capability or observed replication of certain task sequences. The
difference between adaptively and adaptability is that the user plays an explicit role in
adaptability but his role in an adaptive interface is more implied (Dix et al., 1993). 2.5.3 Robustness
A user engaged with a computer in order to achieve some goals in that specific business
domain. The robustness of that interaction comprises features that support the
successful achievement and assessment of the goals. Here, we will discuss the
principles which support robustness. 27 Observability
Observability refers to allow the user to assess the internal state of the system by
perceivable representation at the interface. Observability permits the user to compare
the current observed state with his intention and within the task action plan with a
possibly to lead plan revision. In addition, there are five other principles e.g.
browsability, defaults, reachability, persistence and operation visibility which greatly
helps to understand observability (Dix et al., 1993).
The users mistakes while using a system which they want to recover are called
recoverability. Recoverability allows user to reach their desired goal after recognizing
errors in previous interaction. There are two ways in which recovery can be made,
forward and backward. Forward error recovery covers the current state and negotiation
from that state toward the desired state. Forward error recovery could be the only
possibility for recovery if the effects of interaction are not revocable. Backward error
recovery is a way to undo the effects of earlier interaction in order to return to a prior
state before proceeding. For example, in word-processing, a mistyped keystroke may
wipe out a large section of text which user want to retrieve by an equally simple undo
button (Dix et al., 1993).
Responsiveness is the ability to measures the rate of communication between the system
and the user. Response time is generally the duration of time needed by the system to
express state changes to the user. In overall, short duration and instantaneous response
times are desired. Here, instantaneous means that the user perceives system should react
immediately. However, even in such situations when an instantaneous response is not
obtained, there must be some hint to the user that the system has received the request
and working on request (Dix et al., 1993).
Task conformance refers to the extent the system provides services to all of the tasks the
user wants to perform and the way the user understands them. Task conformance deal
with the coverage issues and task adequacy focus on the users understanding of the
tasks (Dix et al., 1993). 28 2.6 Usability Engineering The principle of usability engineering approach is to know the exact criteria, which can
be used to assess a product for its usability. The user experience about a specific product
is the ultimate key to measurement the usability of that product. Since, a user’s hand on
experience with an interactive system is at the physical interface; therefore the focus on
the actual user interface is logical. With reference to software development life cycle,
one of the significant features of usability engineering is the addition of a usability
specification and formatting the requirement specification that focus on features of the
user-system interaction which contribute to the usability of the product (Dix et al.,
The key feature of usability engineering is the assertion of clear usability metrics early
in the design process, which can be used to assess a system when it is delivered. There
is a logical and solid reason which point out that it is only through empirical approaches
that can be use with usability metrics that we can reliably build more practical systems.
However, the ultimate standard for determining usability might be by observing user
performance, although this does not mean that these measurements are the best way to
produce a predictive design process for usability (Dix et al., 1993).
According to Grudin et al. (1989) usability applies to the growth and expansion of ent...
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This document was uploaded on 12/31/2013.
- Fall '13
- The Land