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2.4 Interface metaphors 59

(b)
Figure 2.10 Two virtual calculators where (a) has been designed too literally and
(b) more appropriately for a computer screen.

Limits the designer's imagination in conjuring up new paradigms and models.
Designers may hate on "tired" ideas, based on well known technologies, that they
know people are very familiar with. Examples include travel and books for repre-
senting interaction with the web and hypermedia. One of the dangers of always
looking backwards is that it restricts the designer in thinking of what new function-
ality to provide. For example, Gentner and Nielsen (1996) discuss how they used a
book metaphor for designing the user interface to Sun Microsystems' online docu-
mentation. In hindsight they realized how it had blinkered them in organizing the
online material, preventing them from introducing desirable functions such as the
ability to reorder chapters according to their relevance scores after being searched.
Clearly, there are pitfalls in using interface metaphors in interaction design. In-
deed, this approach has led to some badly designed conceptual models, that have
resulted in confusion and frustration. However, this does not have to be the case.
Provided designers are aware of the dangers and try to develop interface
metaphors that effectively combine familiar knowledge with new functionality in a
meaningful way, then many of the above problems can be avoided. Moreover, as
we have seen with the spreadsheet example, the use of analogy as a basis for a con-
ceptual model can be very innovative and successful, opening up the realm of com-
puters and their applications to a greater diversity of people.