Hyper-Document structure: representing cognitive coherence in non-linear documents

discourse structure: visual versus textual Abstract features transform the line of text into a visual configuration capable of conveying discourse structure on the space of the page. In visual configurations, the association between a sign and its meaning is characterized by a degree of isomorphism, which makes this association partially motivated. For instance, in the sentence ‘I had a busy morning: I had a work meeting; I went shopping; I picked up the children’, the text segments in the list play an equivalent role within the sentence. This rhetorical equivalence could be expressed through a bulleted list in which the segments are given the same visual rendering: each segment after the colon starting on a new line with a bullet. Likewise, the titles of the sections of a text will be visually more prominent than the titles of the subsections, in order to render the hierarchy of the text structure. Finally, emphasis is visually expressed through a format that stands out. Unlike textual representations, visual representations tend to be regulated by conventions that are less strict and more dependent on the context of use. For instance, a list of clauses could be indented or not, bulleted, numbered or scored; whatever the chosen configuration, it is important that all listed clauses are rendered in the same way and occupy the same horizontal position. Also, the chosen convention should be consistently used throughout a document. Even though they respond to flexible conventions, visual features can express discourse connections so effectively that the use of discourse markers or punctuation becomes redundant. So, in a bulleted list the use of connectives, lineterminal commas or full stops are superfluous, because the conventions at work in the visual configuration of the list override the conventions that regulate the use of discourse connectives and punctuation.features transform the line of text into a visual configuration capable of conveying discourse structure on the space of the page. In visual configurations, the association between a sign and its meaning is characterized by a degree of isomorphism, which makes this association partially motivated. For instance, in the sentence ‘I had a busy morning: I had a work meeting; I went shopping; I picked up the children’, the text segments in the list play an equivalent role within the sentence. This rhetorical equivalence could be expressed through a bulleted list in which the segments are given the same visual rendering: each segment after the colon starting on a new line with a bullet. Likewise, the titles of the sections of a text will be visually more prominent than the titles of the subsections, in order to render the hierarchy of the text structure. Finally, emphasis is visually expressed through a format that stands out. Unlike textual representations, visual representations tend to be regulated by conventions that are less strict and more dependent on the context of use. For instance, a list of clauses could be indented or not, bulleted, numbered or scored; whatever the chosen configuration, it is important that all listed clauses are rendered in the same way and occupy the same horizontal position. Also, the chosen convention should be consistently used throughout a document. Even though they respond to flexible conventions, visual features can express discourse connections so effectively that the use of discourse markers or punctuation becomes redundant. So, in a bulleted list the use of connectives, lineterminal commas or full stops are superfluous, because the conventions at work in the visual configuration of the list override the conventions that regulate the use of discourse connectives and punctuation. Coherence representation in non-linear text Discourse markers such as connectives can only be effectively used when discourse units (clauses, sentences, sections) are arranged in a predefined sequence, so that they are accessed in a univocal order. However the order in which discourse parts will be accessed can only be partly controlled in hypertext, because this is a network of interconnected nodes. Order can be established locally (a node can be linked to another node), but it is hardly possible to establish it globally through a whole hypertext (unless one resorts to constrained paths, which would defeat the purpose of using a non-linear medium). So, discourse markers cannot be used to signal the discourse relation between nodes, because each node is accessible in more than one way. Things, however, are different for abstract document features, because they are visual and work in space. Because of its technical characteristics, hypertext is a spatial medium (and indeed numerous proposals that tackle the issue of non-linearity seek to compensate for the lack of control on discourse order by exploiting the spatial nature of hypertext (compare Carter, 2000). But it is also a temporal medium, in which spatial structures have a temporal dimension and realization (Luesebrink, 1998). Thus, both space and time can be exploited in hypertext to express discourse coherence: in hypertext the notion of abstract document structure includes both spatial and temporal configurations working in a three-dimensional space. We propose that graphics and animation could be used to express discourse coherence in hypertext. At present, most hypertexts (especially on the web) make no use of graphical features to signal rhetorical relations between nodes, and nodes often consist of long text pages with a few links targeting other pages, from 234 Clara Mancini and Donia Scott where the source page can no longer be seen. However, if hypertext nodes were made much smaller, then the screen could be used as a visual field across which they can distribute as links are clicked and new nodes appear, composing meaningful patterns. The appearance and distribution of the nodes should signify the rhetorical role that their content plays within the discourse. To achieve this, rhetorical relations could be used as document structuring principles during discourse construction to define hypertext links. These could then be dynamically rendered during navigation through the consistent and concurrent use of the medium’s spatial and temporal graphic features. In this respect, having established a parallel between textual and visual processing (Riley & Parker, 1998), Gestalt theory has proposed useful principles of document design (Campbell, 1995). Furthermore, a number of representational rules for visually expressing discourse relations between hypertext nodes can be derived from the semiology of graphics, according to which graphic features can be employed to express conceptual relationships of similarity, difference, order and proportion exploiting the properties of the visual image (Koch, 2001). Using these rules, we have designed and begun testing a series of prototype visual patterns expressing coherence relations in non-linear discourse (Mancini, 2005). Still in its infancy, this work aims to identify ways of presenting hypertext discourse which employ graphical features in a systematic and principled way, extending the notion of abstract document structure by making articulate use of the space-temporal dimensions of the electronic medium.