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3.1 Identify the metaphor

Carroll and Thomas have established that people develop new cognitive structures by metaphorically extending old ones [Carroll, 1982]. Users of a new computer system can master it if they can metaphorically extend it to some real world objects or entities. A good metaphor not only helps the user, but also provides a rigid framework within which the hypertext author or designer must work to maintain consistency. Choosing an appropriate metaphor would also reduce both functional opacity (mismatch between the framework and the metaphor) and system opacity (mismatch between the metaphor and the implementation model) [Rao & Turoff, 1990]. Hypertext has been compared to electronic encyclopedia, notecards, journeys, browsing, windows, paths, guided tours, travel holiday, and survey-type maps [Edwards & Hardman, 1989][Hammond & Allinson, 1987][McAleese, 1989]. The travel metaphor serves as an extremely powerful aid to hypertext navigation [Baird, 1989]. At the same time, metaphors should not become too restrictive. Hammond and Allinson say that “the system should improve upon the metaphor, not be bounded by it.” [Hammond & Allinson, 1987].

The metaphor suggested by this framework is “the general cognitive model of how individuals think about complex problems.” [Turoff et al., 1991]. In order to understand hypertext, designers must understand writing and reading models. According to the Cognitive Framework for Written Communication, writing is a combination of three activities: exploring, organizing, and encoding [Smith & Weiss, 1987]. Writing is the transformation of a network of related concepts (retrieved from long-term memory or external sources) into an outline or a hierarchy which is later encoded into a linear sequence of words, sentences, paragraphs, sections, chapters, and illustrations. Reading is the execution of the above three processes in the reverse order. That is, a linear sequence of text is transformed into a hierarchy which is later integrated into a network in long-term memory. Thus, both reading and writing processes are based on the non-linear nature of thinking, a natural process in human beings. Human cognition is essentially organized as a semantic network in which concepts are linked together by associations. Hypertext systems should try to exploit this basic nature of cognition.