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User Modeling for Personalized Web-Based Systems 219
its updates and a source which contributed the characteristic to the model. Each characteristic
contributes to certain user’s goal with certain relevance.
Because characteristics stored in a model are only estimations of real user features based
on analysis of user’s behavior [6], each characteristic has a confidence, informing about quality
of the estimation.
Complete description of the model can be found at http://nazou.fiit.stuba.sk.
User model in OntoAIMS system. Ontology-based Adaptive Information Management
System (OntoAIMS) provides environment for navigation in and searching for information.
This environment recommends its users (students) the most suitable tasks and helps them
in exploration of the domain [23]. System represents the typical example of employment of
ontologies representing a domain as well as user model. User model, created and maintained
by a specialized component OWL-OLM, is forming a layer on the top of a domain model and
adds user’s perspective to it. This approach is suitable in this case, as the information space
defined in domain model (OS Linux course) is closed and static enough. User model is built
using an interactive dialogue with a user and contains information about each individual
concept like number of concept’s usage, number of correct usages, number of times user
declared concept as understood etc. The model is consequently used to recommend content.
Conclusions on User Model Representation
Ontology is clearly the most promising alternative to represent user model. The basic ide
of ontological modeling is very similar to the way how human think about things in the
world. This allows for inclusion of domain experts into to the process of domain and user
model creation. OWL language is expressive enough to capture even complex relationships
present in reality. Ontologies are the basis for inference mechanisms, which could not only
verify model consistency, but are also able to use conditions, restrictions and rules to infer
new relationships and knowledge. Advantage of ontologies is its shareability, supported by
mapping means provided by OWL.
Disadvantage of ontology based representation is currently the lack of tools and technologies,
(editors, mappers, repositories etc.) in the production-grade quality, which would
provide the same efficiency of work as it is with relational databases and XML-based technologies.
8.2 User Characteristics
When designing adaptive web-based system (and its user modeling part) we need to consider
which features of users will be used for adaptation and thus should be modeled. Five most
popular and useful features are [15]: knowledge, interests, goals and tasks, background and
individual traits.
Knowledge is used mainly in adaptive educational systems, which keep track of user’s
knowledge of the domain as a whole as well as of smaller fragments. Interests (keyword or
concept-based) are becoming important as volume of information space increases and new
information-oriented systems (encyclopedias etc.) are being developed.
Goals and tasks represents the immediate purpose for a user’s work within an adaptive
system [15]. It can be a learning goal or immediate information need.