Peter Brusilovsky

Human-Computer Interaction Institute, School of Computer Science,
Carnegie Mellon University, Pittsburgh, PA 15213, USA

World Wide Web opens new ways of learning for many people. Currently, educational programs and learning materials installed and supported in one location can be used by thousands of students from all over the world. This paper presents an electronic ACT-R bookshelf, a system which supports learning ACT-R over the WWW.

ACT-R bookshelf is a collection of electronic books on various aspects of ACT-R. Currently, the bookshelf contains an ACT-R tutorial, ACT-R 4.0 User Manual, a Manual for ACT-R Lisp-based environment, and ACT-R Glossary. The books on ACT-R bookshelf are authored and served on the WWW with InterBook system (Brusilovsky, Schwarz & Weber, 1996). Unlike most existing electronic textbooks which are not more than a static electronic copy of a regular textbook: chapter by chapter, page by page, picture by picture) most of the books on ACT-R shelf are adaptive. Adaptivity is especially important for educational programs on WWW which are expected to be used by very different classes of students without assistance of a real teacher (who usually can provide adaptivity in a normal classroom).

This paper uncover concept-based knowledge representation behind adaptive electronic textbooks (ET) on the Bookshelf, describes main functionality of the system and speculate about possible extensions of the Bookshelf.

Our adaptive textbooks use knowledge about its domain (i.e., ACT-R) represented in the form of domain model and about the students represented in the form of individual student models. The domain model serves as a basis for structuring the content of an adaptive ET. We distinguish two content parts in each adaptive ET: a glossary and a textbook .

According to our approach, the key to adaptivity in an adaptive ET are the domain model and the student model. ACT-R bookshelf uses the simplest form of domain model: a set of domain concepts. By concepts we mean elementary pieces of knowledge for the given domain identified by a domain expert. A more advanced form of the domain model (a network with nodes corresponding to domain concepts and with links reflecting several kinds of relationships between concepts) could support more functionality, but it is hard to develop. The domain model provides a structure for representation of the student's knowledge of the subject. For each domain model concept, an individual student's knowledge model stores some value which is an estimation of the student knowledge level of this concept. This type of model (called an overlay model) is powerful and flexible: it can independently measure the student's knowledge of different topics.

The glossary is the central part of the ET. According to our approach, the glossary is considered as a visualized (and externalized) domain network. Each node of the domain network is represented by a node of the hyperspace, while the links between domain network nodes constitute main paths between hyperspace nodes. The structure of the glossary resembles the pedagogical structure of the domain knowledge and, vise versa, each glossary entry corresponds to one of the domain concepts. The links between domain model concepts constitute navigation paths between glossary entries. Thus, the structure of the glossary resembles the pedagogic structure of the domain knowledge. In addition to providing a description of a concept, each glossary entry provides links to all book sections which introduce or require the concept (Figure 1). This means that the glossary integrates traditional features of an index and a glossary.

Figure 1: A glossary window showing a "page" for chunk type.

A human-written ET represents human teaching expertise on how to introduce the domain concepts to the learners. It is usually a real textbook represented in hypermedia form. Each ET is hierarchically structured into units of different level: chapters, sections, and subsections. Several ET on the same subject form a bookshelf. To make ET "more intelligent" and to connect it to the glossary, we have to let the system know what each unit of the textbook is about. It is done by indexing of textbook units with domain model concepts. All books from the same bookshelf are indexed with the same set of domain model concepts. We use role-based indexing (Osin, 1976). Each terminal unit has an attached list of related concepts (we call this list spectrum of the unit). For each involved concept, the spectrum represents the name and the role of the concept in the unit. Currently we support two roles: each concept can be either a outcome concept or a prerequisite concept. A concept is included in the spectrum as a outcome concept if some part of this unit presents the piece of knowledge designated by the concept. A concept is included in the spectrum as a prerequisite concept if a student has to know this concept to understand the content of the unit. As a part of our approach we suggest to visualize unit indexes, i.e., to show the set of outcome and prerequisite concepts of a unit on a concept bar near the content of the unit. The system has an option to show all outcome and background concepts for the current section on a page border to the right of the section content (figure 2)

Figure 2. A section of ACT-R tutorial as it is presented by Netscape browser. Concept bar (left) shows outcome and background concepts for the section. Navigation center (top) let the user to move in one-click to any section on the same or upper level. Colored balls (up) and checkmarks (right, on the concept bar) provide adaptive annotation.

The knowledge about the domain and about the textbook content is used to serve a well-structured hyperspace. As any well-designed ET, the system supports sequential and hierarchical links for navigation:

In addition the system uses knowledge about the concepts behind the pages to generate other types of links between the glossary and the textbook.:

All these links are not stored in an external format but generated on-the-fly by a special module which takes into account the student's current state of knowledge represented by the student model. This approach is not only reducing page design time but also provides room for adaptation. In particular, our approach supports two adaptation techniques: adaptive navigation support and prerequisite-based help.

Our approach provides many more opportunities for browsing the course materials than traditional on-line textbooks. The negative side of it is that there is a higher risk for the student to get lost in this complex hyperspace. To support the student navigating through the course, the system uses two adaptive hypermedia techniques (Brusilovsky, 1996): adaptive annotation and direct guidance. Direct guidance means that the system can suggest to the student the next unit to be learned. A possible way to provide direct guidance with our approach is presented in (Brusilovsky & Schwarz, 1997). Adaptive annotation means that the system uses visual cues (icons, fonts, colors) to show the type and the educational state of each link.

Using the student model, it is possible to distinguish several educational states for each unit of ET: the content of the unit can be known to the student, ready to be learned, or not ready to be learned (the latter example means that some prerequisite knowledge is not yet learned). The icon and the font of each link presented to the student are computed dynamically from the individual student model. They always inform the student about the type and the educational state of the unit behind the link. In InterBook, red means not ready to be learned, green means ready and recommended, and white means no new information. A checkmark is added for already visited units (Figures 1 and 2). The same way can be used to distinguish and show several levels of students knowledge of the concepts shown on the concept bar. In InterBook, no annotation means "unknown", small checkmark means "known" (learning started), medium checkmark means "learned" and big checkmark means "well-learned" (Figure 1).

The system knowledge about the course material comprises knowledge about what the prerequisite concepts are for any unit of the textbook. Often, when students have problems with understanding some explanation or example or solving a problem, the reason is that some prerequisite material is not understood well. In that case they can request prerequisite-based help (using a special button) and, as an answer to help request, the system generate a list of links to all sections which present some information about background concepts of the current section. This list is adaptively sorted according to the student's knowledge represented in the student model: more "helpful" sections are listed first. Here "helpful" means how informative the section is to learn about the background concepts. For example, the section which presents information about an unknown background concept is more informative than a section presenting information about a known concept. The section which presents information about two unknown background concepts is more informative than a section presenting information about one concept.

A concept-based indexing of ET on ACT-R bookshelf provide a unique opportunity of concept-based linking of various kinds of ACT-R related information. As soon as the ACT-R domain model (a consistent and comprehensive set of ACT-R concepts) is created and all book on the shelf are indexed with ACT-R concepts, these books are invisibly linked through the glossary. Each page of any book which is indexed with a concept will have a link to a glossary entry for this concept. In turn, a glossary entry for a concept will include the links to all pages in all books on the shelf which are indexed with this concept. Currently, the bookshelf contains primary the tutorial and manual-like books. However, we consider several useful extensions of the bookshelf.

There are multiple outcomes of having all ACT-R resources on a single bookshelf interconnected by a global glossary as presented above. Wherever the user starts, he or she can see the concepts behind the pages and see a glossary entry for any of these concepts. A glossary entry for a concept will provide links to all relevant information which exists on the bookshelf. For a introductory-level concept, the user will be able to see book, tutorial or manual pages explaining this concept. For more advanced concepts, the user will also see a list of papers dealing with this concept and a list of people investigating this concept deeply. I think, such an integrated bookshelf accessible worldwide will seriously contribute for the promotion of ACT-R learning and research worldwide.

The work on ACT-R Bookshelf was inspired by John Anderson and his HyperCard ACT-R tutorial. The ACT-R manual and tutorial materials were converted from Word and HyperCard format into HTML format by Valeria Brusilovsky. Elmar Schwarz, the original developer on InterBook, seriously contributed to the development of the Bookshelf. Permanent support of Christian Lebiere, the author of the ACT-R manual was important for the success of the project.