Proceedings of the 12th European Conference on Knowledge ...

Thomas Janke
The rule states that whenever an instance X is related to an instance Y via <strong>the</strong> relation transforms,
<strong>the</strong>n Y is related to X via isTransformedBy. The implication also holds in <strong>the</strong> o<strong>the</strong>r direction.
Both examples <strong>of</strong> ontology patterns show that <strong>the</strong> very same modeling primitives can have very
different representations in various ontology languages.
4.3 Ontology generation based on patterns
The generation <strong>of</strong> concrete ontologies is implemented as a model to model transformation based on
modular patterns. Modularity is a key requirement in this layer. The reasons for that are manifold. The
proposed approach is based on <strong>the</strong> idea that modeling best practices can be provided in an
executable form ready to be applied transparently. This is only possible if <strong>the</strong> platform provides a
framework which allows <strong>the</strong> modular description <strong>of</strong> patterns and <strong>the</strong>refore <strong>the</strong> contribution <strong>of</strong> selfcontained
patterns instead <strong>of</strong> complete transformations. In o<strong>the</strong>r words, various ontology experts
should be enabled by <strong>the</strong> framework to contribute single parts <strong>of</strong> <strong>the</strong> whole transformation. This does
not only lower <strong>the</strong> initial effort necessary to contribute knowledge in form <strong>of</strong> patterns but is also well
aligned to <strong>the</strong> approach followed by <strong>the</strong> ODP community in <strong>the</strong>ir pattern collection wiki (ODP, n.d.).
Moreover, modular patterns introduce room for configurable variability. Certain modeling problems
can be solved by more than one pattern. The W3C, for example, describes two different patterns
(W3C, 2006) for n-ary relations with <strong>the</strong>ir corresponding advantages and disadvantages. In a modular
transformation framework, patterns can easily be exchanged according to specific requirements
without <strong>the</strong> need to edit one monolithic transformation. The Eclipse Modeling Project <strong>of</strong>fers various
model transformation frameworks as candidates to be used to implement <strong>the</strong> ontology generation
layer. The most prominent and widely used frameworks are ATL and Epsilon. Unfortunately, both <strong>of</strong>
<strong>the</strong>m only <strong>of</strong>fer limited support
for pattern modularization and extensibility. Therefore, ano<strong>the</strong>r model
to model transformation framework has been designed and implemented. Its architecture is
introduced in Figure 4.
Figure 4: Model transformation framework based on patterns
The framework consists <strong>of</strong> a number <strong>of</strong> transformations which can be executed by <strong>the</strong> runtime
component. Every transformation contains <strong>of</strong> a number <strong>of</strong> patterns which are applied during
execution. Moreover, every transformation provides helpers that encapsulate functionality used by
multiple patterns and is bound to a number <strong>of</strong> input and <strong>the</strong>ir corresponding output models. Every
pattern is implemented using plain Java. As a result, all IDE features, namely code completion,
debugging, logging, syntax checking etc., are available for pattern development. In order to describe
concrete transformation steps, every pattern defines an arbitrary
number <strong>of</strong> rules whereat every rule is
a plain method with custom annotations provided by <strong>the</strong> framework. Listing 2 illustrates <strong>the</strong> method
signature for <strong>the</strong> n-ary relation pattern discussed above.
@Rule(label="Property2NaryObjectProperty",extend="Property2Property",
priority=1)
public void match(@In Property property,
@Out OWLObjectProperty objectProperty,
@Out OWLClass relationClass)
{ … }
Listing 2: Transformation rule contained in an n-ary relation pattern
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