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According to Laroussi in [Lar 2001] the terms hypertext and hypermedia could be defined using the following three points of view: Semantic, Structural and Functional.

From the Semantic definition point of view, hypertext is considered as an entity that is in turn composed of two more entities: a set of documents and a knowledge structure (see Figure 4.) The poorest representation of this second entity is a link written down inside the first entity, and this is what Nanard calls a “hard link” that joins two documents [Nan 1993].. The most elaborated representation of this knowledge can be generated by a complex system based on domain modeling and user modeling. According to the chosen modeling, the relationship between nodes can be expressed as functional relations or sequences to define a logical structure of documents.

Considering Structural definition, Balasubramanian in [Bal 1994] defines a hypertext as a system composed of nodes and links. The nodes may include textual information (hypertext), or multimedia information such as pictures, diagrams, animations, videos or computer programs (hypermedia). Nodes are joined by links.

Figure 4. Hypermedia documents (adapted from [Lar 2001])

A node is an integrated and self-sufficient unit of information; it is part of a complete hypertext document. The nodes can be considered as origin – the origin of the link (reference nodes) – or as destination – the destination of the link (referred nodes).

A link is an instruction that allows the user to move from the referenced node to the referred node, this is then, a way of traversing the information superhighway. There are different types of links and different actions may be performed from a link. These are stated below.

• A reference link may be used to replace the current node by the new node. • A note link may be used to display the new node in a pop up window while

keeping the current node in the main browser window.

• An expansion link can be used to reveal more information and to branch out in the original space of the link. The link can be reversed, leaving the original one. • A command link enables an action to be performed, such as downloading a file,

or running an executable file.

• An anchor is the visible element, word, phrase or picture that has to be selected to activate the link.

The links can be more or less complex; they can be unidirectional to allow going from one page to another, they can also be marked in order to specify the semantics of the link and, finally, they can be disposed all in one page; however, their roles may sometimes be defined by their position in the document, or by the semantics of the page (i.e., if the page is an index page, the links will enable the

nominated pages). These links define the architecture of the system commonly known as hyperspace [WHATIS].

With respect to Functional definition, hypertext can be considered as a computer process that permits associating a minimal entity (i.e., a word, a portion of a picture or an icon) to another more extended entity (i.e., a paragraph, a picture or a page). Therefore, that mechanism allows the user to move freely in the hypertext. This property of hypertext gives the document interactivity characteristics that a user can take advantage of.

In [Con 1987], Conklin describes several types of hypermedia structure. The most common types use referential links that join two nodes in a non-hierarchical way, resulting in a largely unstructured domain. Referential links are commonly associated with selectable words within a document or as "hot spots" within a graphic. Organizational links may be used, additionally, to connect a node to its parent or child nodes; they are traversed via a separate mechanism from the node itself, either via a graphical browser or via a list of available links. Keyword links or dynamic links search for relevant keywords in the hypermedia current node.

Whether or not it is better to employ non-structured hypermedia (employing referential links), hierarchical hypermedia (organizational links) or a mixture of both is subject to an author’s criteria. The proponents of unstructured hypermedia argue that its unstructured nature provides the richness and freedom associated with hypermedia. However, navigating in such structures exacerbates the well- known problem of cognitive loading [Low 1999] (see details in section II.5). A hierarchical structure is largely dependent on the ability of the defined hierarchy to match the requirements of the user.

A Hypermedia system has been described as a suitable medium for representing structural information (although not all hypermedia systems do). Currently, there is a growing number of systems with information organized on a computer in a structured hypermedia fashion. These systems organize and display information as a meaningful hierarchy instead of a potentially meaningless list of files and directories. Examples of these systems can be observed in:

HIPERBOLIC and SEMIOMAP [Tun 1999] which use Artificial Intelligence techniques to extract information that has been stored within each file so that it may be related to other files in a hierarchical manner. Information is then presented to the user in a structured hypermedia fashion by using a graphical browser interface.

NOTECARDS [Hart 1993] which uses referential and organizational links; although the authors point out that the most common links are organizational.

In PLANG [Fab 2000], a web-based hypermedia environment is used as fundamental support for this thesis proposal which is also based on organizational links. However, the domains employed by the authors in these systems were invariably computer science domains.

Other hypermedia systems such as MICROCOSM [Low 1999] and HYPER-G [Mau 1996] also offer structural and referential link types; however, STRATHTUTOR [Kib 1989] offers dynamic link types using pattern matching heuristics to calculate them.

If the above, or similar, systems replace existing browsers then the structured hypermedia paradigm would become familiar to the computer-using population. Moreover, the cognitive overhead associated with using hypermedia would be reduced.