Adaptive Hypertext and Hypermedia Clients of the User Modeling System BGP - MS

This paper first describes the hypertext system KN-AHS which adapts to users’ presumed domain knowledge, and discusses the support that the user modeling shell system BGP-MS can provide for this adaptation. The aim of constructing KN-AHS was to demonstrate the feasibility of user modeling with BGP-MS in a “normal” hardware and software environment that is frequently found in the workplace. Basic hypertext concepts will be introduced and reasons given for why hypertext should adapt to the current user (especially to his/her state of knowledge). A brief overview of those representation and inference components of BGP-MS that are used by KNAHS will be provided, followed by a description of its adaptive user interface. The interaction between the adaptive hypertext system and the user modeling system will be investigated in detail based on a possible dialog with a user. The inter-process communication between KN-AHS and BGP-MS will then be described and related work discussed. A final section discusses recent research that extends the approach of KN-AHS to a hypermedia information system in a the World Wide Web which additionally adapts its presentation to users’ interests, preferences and abilities (including possible handicaps). 1 This is a revised and considerably updated version of [Kobsa et al. 1994]. 2 Adaptive Hypertext and Hypermedia Clients of the User Modeling System BGP-MS 1. Hypertext and adaptive hypertext 1.1 Hypertext Hypertext consists of any number of objects2 that can be linked with one another in a network structure. Therefore, hypertext is not necessarily read in linear (i.e., sequential) order like conventional text, but can be read in a non-linear order by navigating within the hypertext node network. This non-linear linkage of objects represents the basic characteristic of hypertext [cf. Seyer 1991, Kuhlen 1991]. Hypertext obviously follows the browsing paradigm of information access (like in [Pu & Lalanne, Chapter 18; Vassileva, Chapter 19]) rather than the information retrieval paradigm [Petkovic et al., Chapter 2; Stock, Chapter 16]. Gaining information in a non-linear form is not new (see e.g. information search in encyclopedias). Unlike print media, however, the representation of information in electronic form allows the user to directly and comfortably traverse contextual connections. Hypertext has therefore been able to enjoy an increased importance in the last few years, especially as a basis for on-line help systems and electronic encyclopedias. The user-friendliness of many hypertext systems is rooted in their usage of intuitively understandable direct-manipulative interfaces [cf. Kuhlen 1991, Shneiderman & Kearsly 1989]. The user has the possibility of directly manipulating graphical objects with a pointer (e.g. a mouse) without having to use complicated commands. The effect of these actions can be seen immediately on the screen. Direct manipulation can be used, for example, to reach a different node from the node currently shown on the screen. The usual graphical objects used in such navigating operations include mouse-sensitive text passages (hotwords) or buttons (more on this in Section 3). Other important hypertext components are glossaries, indices, and graphical representations of the hypertext structure, which all offer important meta-information about the basic text objects. Recent research supplements associative navigation by controlled navigation and 2 The objects in a hypertext base are not only text documents but can also include non-textual data (tables, graphs, animation, etc.). The term ‘hypermedia’ is commonly used if an audiovisual component is involved. A. Kobsa, A. Nill, J. Fink 3 by search techniques from the field of Information Retrieval, in order to increase the search efficiency [cf. Kuhlen 1991]. 1.2 Adaptive Hypertext Two major problems arise when working with hypertext systems (see e.g. [Brusilovsky 1996]): • Orientation and navigation problems: When navigating in hypertext, users are frequently uncertain as to how to reach their goals. Since users can choose any course within hypertext, they run the risk of losing their orientation. Navigation aids that take users’ goals into account may be helpful. [Kaplan et al. 1993] showed empirically that navigation suggestions based on knowledge about the objectives and the navigation behavior of previous users as well as the goals of the current user can significantly accelerate the current user’s search for information. • Comprehension problems: Since hypertext is frequently read by users with differing knowledge and experience levels, it may at the same time be too difficult and too detailed for laypersons, and too redundant for experts. [Boyle & Encarnacion 1993] showed empirically that an automatic adaptation of hypertext to the user's state of knowledge significantly improves text understanding as well as partially improving search speed. The system KN-AHS3 deals with the second problem and adapts hypertext objects to the current user's state of knowledge. In contrast to other adaptive hypertext systems, the realization of KN-AHS took advantage of existing software products. TOOLBOOK [Asymetrix 1989], a widely available hypertext shell system, offers a powerful tool for the implementation of the hypertext and its user interface, and the user modeling shell system BGP-MS provides a wide variety of representation and inference possibilities that ensure flexible 3 KN-AHS stands for KoNstanz Adaptive Hypertext System. 4 Adaptive Hypertext and Hypermedia Clients of the User Modeling System BGP-MS adaptation. Both tools run as independent software systems on a PC platform and interact via inter-process communication. 2. User modeling using BGP-MS Over the last few years, researchers have tried to develop so-called ‘user modeling shell systems’, since programming user modeling components in application systems is very time-consuming. These shell systems make integrated mechanisms and methods available which are often needed in user modeling systems. One of these shells is BGP-MS4, which is currently under development. From the perspective of the application system, BGP-MS can be regarded as a “black box” that receives information about the user and answers questions posed by the application system concerning current assumptions about the user. In order to realize its adaptive dialog behavior that is oriented on the user’s state of knowledge, KN-AHS utilizes certain services of BGP-MS. The following sections will gradually present the BGP-MS components that are used, and explain their functionality with regard to the adaptation of hypertext by means of examples5. 2.1 Communication between the application and BGP-MS The user modeling component of KN-AHS is not integrated into the application (as is the case for user modeling components in virtually all other user-adaptive systems), but is rather an independent process that communicates with the application. Observations based on user actions will be reported to BGP-MS by the hypertext system (cf. Fig. 1, part a). The application can ask BGP-MS questions about the user (b) and BGP-MS can in return report its current assumptions concerning the user (c). 4 BGP-MS stands for Belief, Goal and Plan Maintenance System [Kobsa 1990]. 5 A more comprehensive description of BGP-MS can be found in [Kobsa & Pohl, 1995] and [BGP-MS]. A. Kobsa, A. Nill, J. Fink 5 BGP-MS Hypertext System Reporting an observation Query concerning assumptions about the user Answer b) a) (bgp-ms-tell (belief s (belief u (:concept CONCEPT)))) (bgp-ms-ask (belief s (belief u (:concept ROLE))))