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Visualisation of learning ontologies
Trent APTED, Judy KAY, Andrew LUM, James UTHER
School of Information Technologies,
University of Sydney, AUSTRALIA 2006
Abstract. This paper describes a novel system designed to build scrutable student
models from minimal information about the student. It uses MECURIO, our tool for
automatic generation of ontologies from online sources. The system takes a simple
statement of the student’s knowledge or interest in a topic. It uses the ontology to
generate a larger set of components for the student model. The student is then able to
scrutinise these inferences with a visualisation tool, VlUM.
1. Introduction
Ontologies will play an important role in many aspects of future teaching systems,
including such diverse tasks as supporting searches for relevant learning objects, generating
teaching elements and supporting reasoning about the learner's knowledge. It is the last of
these that is the particular focus of our work.
Although ontologies have the potential to be very useful, they are generally difficult
and time-consuming to construct manually. We have been exploring ways to automatically
construct a light-weight ontology [1] from existing documents and, in particular, from
existing dictionaries. This has been used in a tool for visualising large student models. The
ontology provides the structure that enables the visualisation tool to operate effectively.
The user can select a focus concept on the display and the ontology is then used to ensure
that the most closely related concepts are visible. This selection of concepts to be made
visible is an essential part of the visualisation that assists learners in exploring domains
with hundreds of concepts. The particular task we want to support involves showing a user
what an ontology allows us to infer from information such as the learner’s own assessment
of their knowledge.
2. Automated construction of a large ontology
We have used MECUREO [2] to build the ontologies that we use in this project. It
parses a resource such as FOLDOC, the Free On-Line Dictionary Of Computing [3]. The
process results in an ontology of computer science. This is represented as a weighted
digraph. Each node in the ontology is a concept from the dictionary. Links between these
have weights (0, 1]. These associate a cost with the link, with a smaller weight or cost
meaning that the concepts are more strongly related. Links also have a type. Types have an
associated direction. MECUREO builds a large ontology from FOLDOC: 23,095 concepts
and 57,550 directed relationships, with 55,038 of these between distinct concepts.
Essentially, we use point queries to grow student models. So, for example, if a learner
claims to know the concept Haskell, we make a point query on this term, with a suitable
cost-distance value such as 2.0. This returns a subgraph within the full ontology. We use
this to make additional inferences about the learner’s likely knowledge. Similarly, if a
learner expresses interest in learning about Haskell, we can use the same approach to build
a model of a wider set of likely interests. This approach has the potential to help address the
problems of the narrow bandwidth of communication between the user and the machine.
We now describe how we use this ontology to support visualisation of a user model.
3. Ontology visualisation
VlUM, for Visualisation of Large User Models, can effectively display large user models in
web-based systems [4].
VlUM displays the components of the learner model in a vertical listing. It utilises
perspective distortion to enable users to navigate the user model. At any point in time, the
component with the largest font is the one currently selected. Figure 1 shows three VlUM
screens, each displaying an ontology generated from FOLDOC with the concept Microsoft
Word currently selected.
Topics closely related to the selected component appear in a larger font size, spacing
and brightness than those further away in the underlying graph. We can see related
concepts such as GUI, and MS-DOS clearly. Concepts that are not relevant are bunched
together in a small dimmed font.
Figure 1: The visualisation for a MECUREO generated ontology grown from a point query of the concept
Microsoft Word (currently selected) with depth slider set at 1, 2 and 3 from left to right. The depth slider
controls the number links out from the focus concept. The greater the value, the more concepts appear on the
display.
Users can navigate through the model by clicking on a concept to select it. The
display changes so that the newly selected concept becomes the focus. It now appears as
the largest word and a new spanning tree from that concept is generated.
4. Evaluation
We designed MECUREO so that we could take a small amount of information about a user,
since it is common that this is all that is practically available, and use this information to infer
many more things about the user. The role of VlUM is to make that new user model available
to the user so that they can scrutinise it. In particular, we would like users to be able to check
that they are happy with the inferences that have been made.
We have performed a qualitative experiment designed to determine whether users could
indeed make effective use of this display. The participants in the evaluation were five upper
high school students attending a summer school in which they would learn to program in
Python, and five undergraduate computer science students. We asked them to perform tasks on
an ontology from a point query on Python. These users are representative of a quite computer
literate group. Overall, the experiment indicated that the participants could readily
appreciate the general principle of the system, taking a single piece of user input and using
that to generate a much larger user model. All appeared to be able to use it effectively for
the experiment.
5. Conclusions
There are several innovative aspects to the work we have described. First, there has been
very little work on building ontologies automatically from existing resources such as
disctionaries and much that has been done has used much heavier weight approaches, as for
example Kietz et al [5]. There is also the challenging task of evaluating ontologies. A third
contribution of this work is its exploration of visualisation of large user models. There has
been some work on visualisation of a single node and its neighbours in a student model by
Zapata-Rivera and Greer [6]. The combination of all these elements is a further innovation.
The qualitative evaluation we have described is rather limited. It was also designed
to be easily understood by users in a short period of time. So, it does not directly assess
issues of student learning. The importance of our work, for learning, follows from the range
of research on supporting learning through reflection on the student model, such as
explored by Dimitrova et al [7], Bull [8] and Self [9]. Even so, our evaluation indicates the
promise of the approach. It also indicates that the participants in our study could make
sense of the task and could use the VlUM display to explore the ontology. They also shared
our appreciation of the power of this approach to building detailed learner models from
minimal user input.
References
1. Mizoguchi, R., Ontology-based systemization of functional knowledge. 2001.
2. Apted, T. and Kay, J. Automatic Construction of Learning Ontologies. In: L. Aroyo and D. Dicheva,
Editors. International Conference on Computers in Education; 2002. Technische Universiteit
Eindhoven, p. 55-62.
3. FOLDOC: The Free Online Dictionary of Computing, 2001, Available at http://www.foldoc.org/.
4. Uther, J., On the Visualisation of Large User Model in Web Based Systems, PhD Thesis, 2001,
University of Sydney.
5. Kietz, J.-U., Volz, R., and Maedche, A. Extracting a Domain-Specific Ontology from a Corporate
Intranet. In: C. Cardie, et al., Editors. Computational Natural Language Learning and of the Second
Learning Language in Logic Workshop; 2000, p. 167-175.
6. Zapata-Rivera, J.D. and Greer, J., Inspecting and Visualizing Distributed Bayesian Student Models, in
G. Gauthier, C. Frasson, and K. VanLehn, Editors, Intelligent Tutoring Systems. 2000. p. 544-553.
7. Dimitrova, V., Self, J.A., and Brna, P. The interactive maintenance of open learner models. In:
International Conference on Artificial Intelligence in Education; 1999, p. 405-412.
8. Bull, S., Brna, P., and Pain, H., Extending the scope of the student model. User Modeling and User-
Adapted Interaction, 1995. 5(1): p. 44-65.
9. Self, J.A., Open sesame?: fifteen variations on the theme of openness in learning environments.
International Journal of Artificial Intelligence in Education, 1999. 10: p. 1020-1029.
Acknowledgements
We would like to thank Hewlett-Packard for funding parts of this research.