ACM Computing Surveys
31(4), December 1999,
http://www.acm.org/surveys/Formatting.html. Copyright ©
1999 by the Association for Computing Machinery, Inc. See the permissions statement below.
Adaptive Hypermedia: From Systems to Framework
Eindhoven University of Technology
Carnegie Mellon University
Eindhoven University of Technology
1 IntroductionAdaptive hypermedia is a direction of research on the crossroads of hypertext (hypermedia) and user modeling. The goal of this research is to improve the usability of hypermedia. Adaptive hypermedia systems build a model of the goals, preferences and knowledge of the individual user and use this throughout the interaction for adaptation of the hypertext to the needs of that user.
A "classic" hypermedia application serves the same pages and the same set of links to all users. This is true even for most applications that are built on top of systems that are capable of presenting different views to different users. Adaptive Hypermedia Systems (AHS) make it possible to deliver "personalized" views or versions of a hypermedia document (or hyperdocument for short) without requiring any kind of programming by the author(s). Also, although it is possible to offer users a way to initialize the user model through a questionnaire, an AHS can do all the adaptation automatically, simply by observing the browsing behavior of the user. (There are many adaptable systems that allow "personalized" views based on user-selected stereotypes like "beginner" and "expert", or based on interface and style preferences. Another paper in this issue [Quentin-Baxter 2000] deals with this issue in an educational context. The crucial differences with AHS are that in an AHS the adaptation uses a much more fine-grained user model and that the adaptation is done automatically instead of being "selected" by the user.)
A number of adaptive hypermedia systems (AHS) have been developed. The application areas for these systems range from educational hypermedia to information retrieval systems with a hypertext interface. Various research groups have developed different original techniques to adapt aspects of hypermedia systems to individual characteristics of a user. A comprehensive review of adaptive hypermedia techniques and systems can be found in [Brusilovsky 1996]. In Section 2 we briefly review some popular methods and techniques for AHS. Some adaptive hypermedia applications have been empirically evaluated. Experiments have been conducted to test whether information can be found faster or can be better comprehended when adaptive techniques are used. Section 3 reports on such evaluations.
2 Framework, Methods, and Techniques for Adaptive Hypermedia
2.1 A Framework for Adaptive HypermediaThe authors independently developed a similar framework to describe adaptive hypermedia applications. In this framework the "knowledge" contained in a hyperdocument is described by a domain model:
2 2Adaptive PresentationAdapting the presentation of information within a page is most often performed as a manipulation of (canned) text fragments. The aim of these manipulations can be:
2.3 Adaptive Navigation SupportThe manipulation of links that are presented within nodes (pages) is typically done in one or more of the following ways:
3 Evaluation of Adaptive Hypermedia ApplicationsWhether the use of adaptive hypermedia (presentation and/or navigation) is beneficial, for comfort or performance, is always a combination of the adaptive methods and techniques that are used and of the way in which the adaptation is used. (One could use adaptive techniques to guide users in the wrong direction and turn navigation through a hyperdocument into an adventure game.) Below we describe some evaluations of adaptive hypermedia applications. We do not (and cannot) imply that these results would carry over to all applications that use the same adaptive techniques.
3.1 Evaluation of adaptive presentationThe most comprehensive evaluation of adaptive presentation in hypermedia was performed by Boyle and Encarnacion [Boyle 1994] with their adaptive stretchtext system MetaDoc. (See subsection 2.2 for a description of stretchtext.) The three systems that were compared are the original MetaDoc with all functionality and two "disabled" versions of MetaDoc: the stretchtext version which had all stretchtext functionality, but no user modeling and adaptation and the hypertext-only version which had no stretchtext functionality at all. Two kinds of tasks were used to compare these kinds of hypertext: eight reading comprehension tasks and five search and navigation tasks.
The experiment shows that the users of the adaptive stretchtext version have found answers to comprehension questions significantly faster than users of the traditional hypertext version while showing significantly better comprehension. No significant difference was found regarding the performance in solving search and navigation questions (search correctness, number of visited nodes, and number of operations).
3.2 Evaluation of adaptive navigation supportBrusilovsky and Pesin conducted one of the earliest studies of adaptive link annotation and link removal mechanisms using their system ISIS-Tutor [Brusilovsky 1998a]. ISIS-Tutor uses the dynamic state of user knowledge represented in the user model to classify all concept and task nodes into several classes such as not ready to be learned, ready to be learned, well-learnt and in work. Adaptive link annotation (color fonts and special symbols) was used to show classes of pages behind links. The study compared three versions of ISIS-Tutor: a non-adaptive version, a version with adaptive annotation, and a version with both adaptive annotation and adaptive link removal (link anchors for not ready to be learned pages were removed.) The study (performed with 26 first year computer science students) showed that the overall number of navigation steps, as well as the number of unforced repetitions of concept and task pages were significantly lower with both adaptive versions of the system. No difference was found between the link annotation with or without the additional link removal technique. No difference was also found between all three groups for the quality of mental maps of the hyperspace developed by students.
A similar study involving 25 undergraduate "teacher education" students was performed with the InterBook system [Brusilovsky 1998], a Web-based descendant of ISIS-Tutor. The study compared two versions of the system: with and without adaptive link annotation. The trial had some clear limitations. Since the non-annotated "continue" link (which takes the user to the next page) was used in over 90% of transactions, the effect of link annotation on student paths was relatively small. However, the study showed that link annotation encourages the novices to use non-sequential links more often. The study also showed that the students who follow the system's guidance are able to achieve better post-test scores.
4 Conclusions and Future TrendsIn this paper we presented a framework for adaptive hypermedia systems. We considered domain modeling and user modeling and showed methods and techniques for adaptation of hypertext, notably adaptive presentation and adaptive navigation support. Examples of adaptive hypermedia systems are described, including evaluations of the adaptation in those applications.
Future developments include a generalization to adaptation in nodes other than text nodes and the creation of standards for adaptive hypermedia systems to communicate with each other (in order to exchange information on users between different applications). More experiments need to be done to evaluate the benefits of adaptive hypermedia in different application areas.
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