Methodology II: Cognitive Dimensions and the Gulfs - Foundations for Designing User-Centered Systems - page 332

know that it would do something if I clicked there?'' This effect is particularly
found on those web pages where banners and logos are designed as clickable
images, but users more commonly (and more naturally based on their experience)
perceive them as just being graphical images.
A piece of program code with well-chosen variable names can be very role-
expressive. The goals of the programmer in each statement can be made readily
apparent to the reader if the functions and variables are given names that clearly
indicate their purpose. 1
The Microsoft Excel spreadsheet application also supports role expressiveness.
When you add a formula to a particular cell, for example, it color codes the cells
that are referenced by that formula. Note that the color coding only happens as the
formula is created, and disappears when you calculate the result of evaluating that
formula.
Classic problems of role-expressiveness occur where two similar looking fea-
tures achieve different functions or where two different looking functions achieve
similar effects. That is, where the role-expressiveness for two similar looking
objects is different, or where the function of two different looking objects appears
the same. For example, the Border and shadings functions in some older versions
of Microsoft Word can be accessed using the top level menu but also appear in
three other places in the interface, with different sets of functions available to the
user in each place with differing effects. This can confuse users who fail to dis-
tinguish between paragraph borders and table cell borders because Word displays
them in apparently unpredictable ways.
There may sometimes be a conflict between role-expressiveness and consis-
tency. Designing a system to be role-expressive will usually mean using a richer
vocabulary with less (apparent) uniformity. A good way to resolve this conflict is
to carry out a clear and effective analysis of the users' tasks and the importance of
learning versus other measures of usability rather than focusing solely on con-
sistency (Grudin 1989 ). Role expressiveness might also be poor on purpose to
encourage exploration. This may occur in games or educational software and
hardware (Yeh et al. 2010 ).
12.2.4 Premature Commitment
The point at which users have to commit to taking a particular action varies across
environments and systems. For example, when you go into a café you sometimes
find that you have to select which cutlery you need before you have seen what food
is on offer that day. Until you know this you will not know whether you will need a
1 Jonah Gregory (personal communication, 2008) notes that programmer's comments can be
helpful in these situations, and we agree. However, comments can also be a nightmare because
they often do not get updated when the code changes. So, there are design decisions about when
to update and how to update such documentation.