AHAM: a Dexter-based reference model for adaptive hypermedia

Hypermedia applications offer users the impression that there are many meaningful ways to navigate through a large body of information nodes. This rich link structure not only creates orientation problems, it may also be a source of comprehension problems when users follow paths through the information which the author did not foresee. Adaptive techniques have been used by a number of researchers [1, 2, 4, 5, 6, 7, 8, 9, 10, 17, 19, 20, 22] in an attempt to offer guidance through and orientation support for rich link structures. The majority of these adaptive hypermedia systems (AHS) have been used in educational applications. The terminology used in this paper also has an educational “flavor”. However, there are some adaptive on-line information systems (or “kiosk”systems), adaptive information retrieval systems, and other adaptive hypermedia applications. In this paper we describe a reference model for adaptive hypermedia applications, called AHAM, which encompasses most features supported by adaptive systems that exist today or that are being developed (and have been published about). Our description of AHS is based on the Dexter model [15, 16], a widely used reference model for hypermedia. The description is kept somewhat informal in order to be able to explain AHAM rather than formally specify it. AHAM augments Dexter with features for doing adaptation based on a user model which persists beyond the duration of a session. Key aspects in AHAM are: Paul De Bra is also affiliated with the University of Antwerp, Belgium, and with the “Centrum voor Wiskunde en Informatica” (CWI) in Amsterdam. yGeert-Jan Houben is also affiliated with the University of Antwerp, Belgium, and with Origin in Eindhoven. The adaptation is based on a domain model, a user model and a teaching model which consists of pedagogical rules. We give a formal definition of each of these (sub)models (but only describe the pedagogical rules informally throughexamples). We distinguish the notions of concept, page and fragment. In some AHS these notions are confused. We provide a formalism which lets authors write pedagogical rules (about concepts) in such a way that they can be applied automatically. We illustrate various aspects of AHAM by means of some features of some well-known AHS [6, 10].