PEGASUS: A Domain-Independent Presentation

Modeling System for Context-Sensitive Hypermedia


Pablo Castells and José Antonio Macías

Summary

With the rapid development of computer-based online education, learners are gaining increasing autonomy, and instructional applications are reaching an unprecedented diversity of users and platforms. In this context, considerable efforts have been made towards the development of web-based applications that adapt automatically to student and platform characteristics, taking into account the evolution of each user over time. A common (explicit or implicit) primary concern to all research work in this area is that of finding an appropriate representation for domain and instructional knowledge.

PEGASUS (Presentation modeling Environment for Generic Adaptive hypermedia SUpport Systems) is a generic presentation system for adaptive hypermedia that makes minimum assumptions about how domain and instructional knowledge are represented. It provides courseware designers with a simple specification paradigm for non-trivial adaptive presentation constructs, that can be used with different course management systems. In order to allow for different approaches, PEGASUS supports the definition of made-to-measure domain ontologies for the description and conceptual structuring of subject matter. Domain ontologies consist of a set of classes and semantic relations for knowledge representation that best suit the nature of a specific domain or that reflect the particular vision of a specific author on the domain. Once an ontology is defined, designers build courses by creating domain objects (knowledge units) and relating them together using the conceptual vocabulary defined by the ontology, forming a semantic network. Course presentation is designed by defining an explicit presentation model where presentations are associated to ontology object classes and relations. The definition of an abstract presentation model, separate from course contents, enhances presentation reuse and consistency, thus reducing the development cost.

The PEGASUS presentation model consists of presentation templates and presentation rules. A presentation template describes how to present a domain class. Templates define what parts (attributes and relations) of a knowledge unit must be included in its presentation, their visual appearance and layout. Presentation rules that govern aspects like link generation, correspondence between link styles and topic states, ordering and layout of (fragment or link) lists, and the generation of built-in presentations for topic network subsets like linked lists and trees. Rules simplify template syntax by generating adaptive presentation constructs involving relations between domain objects from very succinct high-level descriptions. Adaptivity is achieved by setting conditions on templates, on parts inside templates, in presentation rules, and over relations between objects in the domain model itself. These conditions can test properties of the user model (overlay model and user profile), characteristics of the platform, and any other aspect that should influence presentation, like course requirements, student’s goals, usage modes (e.g. learning vs. consultation), etc.

At runtime, the student interacts with the application from a web browser. The interaction with an application built with PEGASUS consists of a traversal of the domain object network. In the pages presented to the user, links do not correspond to other pages, but point, explicitly or descriptively, to domain objects. Each time the user moves to an object by traversing a link, PEGASUS responds by creating a new HTML page. In doing so, the system:

  1. Resolves the user’s request determining the domain object to move to.
  2. Finds the actual instance in the domain model.
  3. Updates the domain and user model taking into account the current user action.
  4. Generates the HTML presentation by applying the pertinent rules and the template that corresponds to the class of the domain object.
In general, our presentation system does not work alone, since steps 1 and 3 above are external to PEGASUS. Once an ontology has been defined and the subject matter has been modeled as a semantic network, PEGASUS takes care of how domain and user model updates affect presentation at runtime, but a complementary module is needed to make these updates (step 3), as illustrated in Figure 1, applying pedagogical strategies like the ones used in state-of-the-art adaptive hypermedia support systems. Optionally, a planner can be integrated to determine the path to follow in response to each user request (step 1). Because the dynamic generation of presentation is a separated mechanism from the user and domain model update mechanisms, our presentation system can be used with different underlying courseware support tools.

Figure 1.  Course model and overall architecture

Ease of use is a major concern in PEGASUS. Our system will be complemented with ATLAS, a suite of interactive tools for courseware authoring. We are currently completing the development of a graphic tool for building domain ontologies and domain model semantic networks. We are also starting to devise an authoring tool for presentation, with which authors can customize presentation models by example, by editing generated HTML pages.

PEGASUS is being implemented in JavaTM JDK 1.3, using XML/DOM and JavaServer PagesTM.

PEGASUS is part of the Encitec project, funded by the Spanish government.

Relevant Publications

J. A. Macías and P. Castells.
Tailoring Dynamic Ontology-Driven Web Documents by Demonstration.
Proceedings of the 6th International Conference on Information Visualisation - International Symposium of Visualisation of the Semantic Web.
IEEE Computer Society, London (England), July 2002.
http://www.ii.uam.es/~castells/publications/vsw02.pdf

J. A. Macías and P. Castells.
An Authoring Tool for Building Adaptive Learning Guidance Systems on the Web.
Lecture Notes in Computer Science: Active Media Technology – AMT 2001.
Springer-Verlag, Viena (Austria), 2001.

P. Castells and J. A. Macías.
An Adaptive Hypermedia Presentation Modeling System for Custom Knowledge Representations.
Proceedings of the World Conference on the WWW and Internet (WebNet’2001).
Orlando (Florida), October 2001.
http://www.ii.uam.es/~castells/publications/webnet01.pdf

J. A. Macías and P. Castells.
Adaptive Hypermedia Presentation Modeling for Domain Ontologies.
Proceedings of 10th International Conference on Human-Computer Interaction (HCII’2001), pp. 710-714.
New Orleans (Louisiana), August 2001.
http://www.ii.uam.es/~castells/publications/hcii01.pdf

J. A. Macías and P. Castells.
A Generic Presentation Modeling System for Adaptive Web-based Instructional Applications.
Proceedings of ACM Conference on Human Factors in Computing Systems (CHI’2001), Extended Abstracts, pp. 349-350.
Seattle (Washington), April 2001.
http://www.ii.uam.es/~castells/publications/chi01short.pdf

J. A. Macías and P. Castells.
Interactive Design of Adaptive Courses.
In Computers and Education – Towards an Interconnected Society, M. Ortega and J. Bravo (eds.).
Kluwer Academic Publishers, Dordrecht (The Netherlands), 2001.
http://www.ii.uam.es/~castells/publications/kluwer01.pdf

P. Castells and P. Szekely.
Presentation Models by Example.
In Design, Specification and Verification of Interactive Systems '99, D.J. Duke and A. Puerta (eds.), pp. 100-116.
Springer-Verlag, Viena, 1999.
http://www.ii.uam.es/~castells/Papers/dsvis99.pdf

P. Castells y J. A. Macías.
Un sistema de presentación dinámica en entornos web para representaciones personalizadas del conocimiento.
Revista Iberoamericana de Inteligencia Artificial No. 16 (2002).
AEPIA, 2002, pp. 25-34.
http://www.ii.uam.es/~castells/publications/aepia02.pdf

J. A. Macías y P. Castells.
Personalización de páginas web dinámicas mediante ejemplos.
III Congreso Internacional de Interacción Persona-Ordenador (Interacción 2002).
Madrid (Spain), May 2002.
http://www.ii.uam.es/~castells/publications/interaccion02.pdf

P. Castells y J. A. Macías.
Un sistema de presentación dinámica hipermedia para representaciones personalizadas del conocimiento.
II Congreso Internacional de Interacción Persona-Ordenador (Interacción 2001).
Salamanca (España), 2001.
http://www.ii.uam.es/~castells/publications/interaccion01.pdf

Page maintained by pablo.castells@uam.es
Last updated: 15-10-01