Phdthesis3016
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KIT
Erscheinungsort / Ort: Karlsruhe
Referent(en): Rudi Studer, Peter H. Schmitt, Pascal Hitzler
BibTeX
Kurzfassung
Formal models of domain-specific knowledge abound in science and technology.
It is desirable that such models can be managed, exchanged, and interpreted in
computer systems, and the term “ontology” was coined to refer to the respective
modelling artefacts. A prominent application field for ontologies is the Semantic
Web where the Web Ontology Language OWL is the predominant modelling language.
The formal semantics of OWL is largely based on the description logic (DL)
family of knowledge representation formalisms that are well-suited for terminological
modelling. Rule-based knowledge representation languages, in contrast, have
a stronger focus on modelling relationships between instances. Both perspectives
are relevant in applications but the combination of rules and DLs turns out to be
difficult, since vital computational properties such as decidability are lost easily.
The subject of this work is to advance the development of hybrid DL rule languages
based on first-order Horn rules. Reasoning for SWRL – the combination
of DLs with (first-order) datalog – is known to be undecidable, and we identify
DL Rules as a novel class of decidable SWRL fragments that is closely related to
DLs. New decidability results for DLs with role constructors allow us to include
simple role conjunction and concept products into DL Rules. DL Rules are further
extended with DL-safe variables to arrive at DL+safe rules. The latter properly
generalise DL Rules and the known approaches of DL-safe rules and role-safe recursive
CARIN.
This leads to expressive DL rule languages with high computational complexities,
motivating the study of more restricted languages. We introduce Horn DLs to
generalise the known DL Horn-SHIQ, and show that many of these DLs exhibit
high reasoning complexities in spite of their low data complexity. DLP has been
proposed as a logic in the “expressive intersection” of DLs and datalog. We question
the meaning of this description, and develop formal design criteria for DLP
that let us specify the largest datalog-expressible fragment of description logics.
Combining these insights, we arrive at a new tractable DL rule language ELP
which extends both DLP and the light-weight DL EL++, although the union of
these languages is intractable. ELP incorporates DL Rules and a certain form of
DL+safe rules, and we present a reasoning procedure based on a direct reduction to
datalog that preserves the structure of rules. This also lets us derive a new datalogbased
inferencing procedure for the DL SROEL(⊓s, ×) which extends EL++.
This work advances the understanding of the relationship of rules and description
logics, leading to concrete new knowledge representation formalisms of practical
relevance. DL+safe rules constitute one of the broadest classes of decidable
SWRL fragments known today. ELP provides a tractable DL rule language that
generalises the novel light-weight ontology languages OWL RL and OWL EL as
standardised by W3C, and that has been adopted as the basis for the WSML-DL
v2.0 dialect of the Web Service Modeling Language. Our work also suggests new
rule-based implementation methods for supporting these languages based on a single
inferencing algorithm.
ISBN: 978-3-89838-643-2
Beschreibungslogik, Logikprogrammierung, Semantic Web