Abstract
We propose a mediator architecture that allows a
learning system to retrieve learning objects (LOs) from
heterogeneous repositories of LOs and not exclusively
from its proprietary repository. A mediating component
accepts queries formulated in a uniform query
language, translates them into repository specific queries
and passes them to each connected repository. For
the translation of queries, an ontology-based queryrewriting
method has been developed which uses the
specified knowledge representation of the repository
and an ontology mapping to compute the rewriting
steps for translating. For distributing queries we realized
a mediating architecture, which passes the translated
queries to the repositories. This architecture has
been integrated in the Web-based, user-adaptive and
interactive e-learning environment ActiveMath. Currently,
it enables the ActiveMath's course planner to
access four heterogeneous LO repositories. The course
planning component can create courses adapted to the
learner's goals, knowledge, learning behaviour and a
specific learning scenario. To select adequate LOs,
the course planner initially queried its proprietary repository
MBase for LOs. The challenge our architecture
faces is to integrate more than one repository into
ActiveMath's course generation. Currently, with the
help of the architecture here-proposed, the course planner
retrieves LOs additionally from the repository of
the DaMiT-system, of the MathsThesaurus, and the
LeActiveMath ExerciseRepository.
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