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Navigation, whereby the user moves through the hypermedia network by following links from node to node is the primary means for accessing information in most Hypermedia systems ( except those which are dedicated to information retrieval applications ) so far. Navigation is a defining feature of Hypermedia systems and critical for characterised them along three fundamental dimensions, scope, target task domain, target user domain. The ability to navigate makes Hypermedia a powerful tool for managing information. Navigation is not something which happens without problems and it is directly related to several hypermedia problems like user dissorientation and cognitive overhead.
People are using schemata or models of the physical enviroment to navigate themselves. This is acquired from experience and afford them a basic oriented frame for navigatory purposes.While schemata are effective oriented guides, in themselves are limited. Schemata are not constitute knowledge but expectation. Another interesting theory about navigation is this of cognitive maps. According to this theory, people represent knowledge which is characterised by the ability to navigate form point A to point B, using landmark knowledge. The next stage of development is the ability to navigate from point A to point B using whatever landmark knowledge we have acquired. The third stage involves the acquisition of survey knowledge. This is a fully cognitive map. Cognitive maps theory, otherwise schemata theory has it is equivalent in Hypermedia space with Hyperbase landmarks.
Although navigation is considered a major issue by many authors, there is a growing body of opinion that suggests its importance is over-emphasized (Kibby, 1992). Hypermedia is for organising information in a loosely structured way and allow users to freely explore and discover required information in the hypermedia environment. In such a context, it is a physical consequence for navigation not to be an easy process. In educational applications of hypermedia the challenge to be disoriented and retreat to familiar web structure, is very important and has the potential to be an efficient learning procedure.
Guided tours offer possible solutions to the navigation problem by eliminating freely explorative navigation. A guided tour is a predefined trail of nodes. Hypermedia users select a guided tour from a list of offered tours and they passively visit all the nodes that are included in tour's trail. Guided tours can be used by hypermedia authors to express, predefined views of how the hypermedia network "should be traversed" for capturing required information.
An important element of navigation control is the ability to retreat from an area of confusion to familiar ground. The simplest way to do so is incorporated in current hypermedia systems by a history and backtracking mechanism. Backtracking is the facility to move along the path of previous visited nodes. The ability to backtrack complements the history mechanism. This mechanism records in a meaningful way all the previous visited nodes.
Bookmarks act a general signs to orient the hypermedia user. The difference between histoty lists and bookmark lists is that a node is inserted in the bookmark list only if the user wants to do so. This condition means that bookmark lists are smaller and thus more manageable than history lists. Bookmarks correspond to landmark knowledge in psychology cognitive map theory of navigation.
Paths is a mechanism for allowing the author to impose a sequence. Path has been introduced as a mechanism for solving navigation problems. The expressive power of apath is determined both by the sequencing model and the characteristic of the entities that can apear along the path. The notion of paths is based on the programming paradigm. Zellweger has described the concept of a path in order to eliminate the influence of link concept in basic hypermedia model.
Navigation around a complex hypertext system is a serious problem because of the largely unstructured nature of hypertext. Experience and empirical studies establish evidence for the impact that structure has to navigation (Botafogo, 1994). Users navigate easier in hyperspace when information is set out in well defined structures. On the other side basic hypermedia model offers a very limited ability for structuring information. Many hypermedia systems employed hierarchical and less of them aggregation structures for improving navigation in their hyperspace.
A metaphor offers a way of conceptualising the interface between a user and a hypermedia system. In general a metaphor is used to conceptualise an object. It is frequently used as an aiding mechanism for aiding novice's comprehend unfamiliar objects. Metaphors are based on the logic that previous acquired experience-schemata can help users in the comprehension of new knowledge.
We can identify two parallel structures in a hypermedia network. One is the set of explicit nodes and explicit links. This structure is called hyperspace. The other is the concept space delineated from explicit and implicit knowledge, embedded in the nodes and links and all possible associations between this information. Navigational tools like browsers help users to navigate in hyperspace but they ignore the concept space which it is developed in parallel with hyperspace. Concept space is more complex than hyperspace because it is based in implicit knowledge. Hyperspace has to do with searching and locating information. Concept space is about comprehension of this information. Concept space is ignored in current hypermedia systems (Hammond, 1993) (Kibby ,1992). Navigate in concept space rather than just in hyperspace could be a crucial factor for the success of hypermedia in some target task domains like instructional hypermedia.
In directed or undirected navigation a hypermedia user explores hyperspace using conversely navigational aiding tools such as browsers, guided tours or just by simple following links. This kind of navigation is guided by user. The term intelligent navigation refers to access where the responsibility for guiding the navigation is distributed between the user and the hypermedia system. An inferencing mechanism is used to support intelligent navigation by constructing paths according to user's queries. To support intelligent navigation hypermedia network is represented by a semantic network. Knowledge is added to nodes and links to allow arbitrary computations and inferencing.