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2.3 Conceptual models 43

Figure 2.3 Two vending machines, (a) one selling soft drinks, (b) the other selling a range of
snacks.

misreading the code and or mistyping in the code, resulting in the machine not issuing the
snack or providing the wrong sort.
A better way of designing an interface for a large number of choices of variable cost is to
continue to use direct mapping, but use buttons that show miniature versions of the snacks
placed in a large matrix (rather than showing actual versions). This would use the available
space at the front of the vending machine more economically. The customer would need
only to press the button of the object chosen and put in the correct amount of money.

Much research has been carried out on how to optimize command-based and
other instruction-giving systems with respect to usabilty goals. The form of the
commands (e.g., the use of abbreviations, full names, icons, and/or labels), their
syntax (how best to combine different commands), and their organization (e.g.,
how to structure options in different menus) are examples of some of the main
areas that have been investigated (Shneiderman, 1998). In addition, various cogni-
tive issues have been investigated that we will look at in the next chapter, such as
the problems people have in remembering the names of a set of commands. Less