Thesis full text (PDF) - Politecnico di Milano

the development complexity is increased, and the usability of the tools is reduced. Finally, only
the KB framework supports deduction and update of the knowledge with dedicated components
and design patterns.
The last table category summarizes the architectural aspects of the tools. All the tools have
methodological support, but except the KB framework, they are difficult to extend mainly
because they base on two-tier architecture. The KB framework is open to extensibility by means
of custom units. Extensions may occur either at the framework logic level providing a new
functionality upon the existing inference system, at the business logic level giving access to the
knowledge base, or at both.
In Table 6.2 a second comparison is made upon the expressive power of knowledge
representation languages (OWL and the language underlying the KB Framework). Both
languages are mapped to formalisms from the Description Logics family. Such comparison
focuses on the main features of each language in knowledge modeling in order to highlight their
differences and their limitations. All of them support the notion of class and class hierarchy;
although the KB Framework Language does not support exhaustive decomposition and
partitioning, due to implementation problems encountered using Pellet. In fact, UML considers
completeness upon generalization sets; therefore, we plan to resolve this limitation in future
releases. Similar is the support of property hierarchies in the languages. Derived support
indicates that the language does not provide a construct for the feature in question, but it supports
it through a combination of other constructs. Attributes that characterize the class are covered
through workarounds: both in OWL and in the KB Framework Language, class attributes are
defined once in the class definition for all the instances of the class. Finally, enumeration of
classes is not yet supported in KB Framework Language, although it is provided in UML. We
plan to extend the implementation to cover this aspect too.
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