Information Technology Reference
In-Depth Information
by only one point. If you want to modify the fonts in a PowerPoint presentation by
one point, then you have to use more detailed tools and it takes longer. You can do
it, but it is more viscous. As another example, iTunes makes it relatively easy to
add a new playlist or to modify a playlist. It makes it more difficult (viscous) to
erase songs.
Two types of viscosity can be differentiated:
• Repetitive viscosity—where what appears to be a single goal has to be carried
out as lots of small, repetitive actions. For example, if you want to change in a
document every number followed by a tab into the same numbers followed by a
space, this has to be done by hand in Word because, while the number can be
found, it cannot be included in the replace, thus increasing the viscosity of
editing Word documents. Similar effects can be found in many systems when
renaming files within a graphical user interface.
• Knock-on viscosity—where what appears to be a single goal requires several
more small changes to restore consistency (e.g., adding a sentence at the
beginning of a document and having to redo all the work involved in ensuring
that appropriate page breaks occur).
Solutions to the problems of inappropriate amounts of viscosity can involve
either redesigning the system or providing tools to help manage the difficulties.
The latter is more likely to be useful where viscosity may be desirable, as a way of
promoting reflective action and encouraging learning. In some cases there may be
a trade-off, however, and making some actions less viscous may lead to others
becoming more viscous. It is also worth noting that it can be useful to deliberately
make some actions viscous, e.g., if there are safety critical elements, or an action
may be dangerous if carried out incorrectly, or they are expensive in time or
money. On the other hand, simple, routine actions should normally be made as
non-viscous as possible.
12.2.3 Role-Expressiveness
Role-expressiveness describes the extent to which a system reveals the goals of the
system's author/designer to the reader/user. It should be easy, for example, for a
reader to see what each component in a program does, and how each component
relates to the whole. This need to infer the other agent's goals and plans is
important, as we noted earlier in
Chap. 7
, with particular reference to how Grice's
maxims describe successful communication.
One obvious example of role-expressiveness is that the buttons on an interface
should be clearly recognizable as buttons that the user can press. In some inter-
faces, however, role-expressiveness is poor because interface objects that are
clickable are not easily recognizable as being clickable—''But how was I meant to
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