Martin Homola

Contextualized knowledge repositories for the Semantic Web

We propose Contextualized Knowledge Repository (CKR): an adaptation of the well studied theories of context for the Semantic Web. A CKR is composed of a set of OWL 2 knowledge bases, which are embedded in a context by a set of qualifying attributes (time, space, topic, etc.) specifying the boundaries within which the knowledge base is assumed to be true. Contexts of a CKR are organized by a hierarchical coverage relation, which enables an effective representation of knowledge and a flexible method for its reuse between the contexts. The paper defines the syntax and the semantics of CKR; shows that concept satisfiability and subsumption are decidable with the complexity upper bound of 2NExpTime, and it also provides a sound and complete natural deduction calculus that serves to characterize the propagation of knowledge between contexts.

AUGMENTING SUBSUMPTION PROPAGATION IN DISTRIBUTED DESCRIPTION LOGICS

Distributed description logics (DDL) enable reasoning with multiple ontologies interconnected by directional semantic mapping, called bridge rules. Bridge rules map concepts of a source ontology into concepts of a target ontology. Concept subsumptions of the source ontology can be propagated according to a propagation pattern expressed by means of bridge rules into concept subsumptions of the target ontology. In the basic formulation of DDL, such a propagation is mostly limited to cases when pairs of ontologies are directly linked by means of bridge rules. However, when more than two ontologies are involved, one would expect that subsumption propagates along chains of ontologies linked by bridge rules, but the semantics of DDL is too weak to support this behavior. In a recent study, an adjusted semantics for DDL that supports subsumption propagation through chains of bridge rules has been introduced. This study makes use of a so-called compositional consistency requirement that has been employed before in package-based description logics. While the results concerning subsumption propagation under the adjusted semantics are encouraging, there are important drawbacks. In this article we take a wider perspective, and propose a study of several different alternative extensions of the DDL semantics. For each of them we study the formal properties, and we select the one that, according to our analysis, constitutes a good compromise, and for this case we provide a sound and complete tableaux decision procedure.

Dynamic logic programming: various semantics are equal on acyclic programs

Multidimensional dynamic logic programs (MDLPs) are suitable to represent knowledge dynamic in time, or more generally, information coming from various sources, partially ordered by arbitrary relevancy relation, e.g., level of authority. They have been shown useful for modeling and reasoning about multi-agent systems. Various approaches to define semantics of MDLPs have been presented. Most of the approaches can be characterized as based on rejection of rules. It is understood that on some restricted classes of MDLPs several of these semantics coincide. We focus on acyclic programs. We show that for a MDLP

Mapping structural design patterns in OWL to ontological background models

\mathcal{P}

Blogging in Obligatory Course: A Bitter Victory

and a candidate model M, if

MKNF Knowledge Bases in Multi-Context Systems

\mathcal{P}

May I Peer-Review Your Web Design Project?

is acyclic to some extent then several of the known semantics coincide on M. It follows as a direct consequence that on the class of acyclic programs all of these semantics coincide.

Peer Review Support in a Virtual Learning Environment

The concerns of efficient data management and logical inference on the Semantic Web often lead to disconnection between the surface structure of RDF/OWL data/ontologies and the background state of affairs. The PURO ontology background model language allows to explicitly capture the mapping between the foreground and background modeling layers. The background modeling primitives are intentionally kept analogous to those of RDF/OWL, namely, derived from the particular-universal and relationship-object distinctions. We project the PURO framework onto the W3C CPV family of structural design patterns, thus providing additional insights into them and possibly facilitating their selection and reuse.

Resolving conflicts in knowledge for ambient intelligence

In the course of several years, we employed blogging assignments in an obligatory web design course. The assignment was able to attract interest of few students only, while the majority did not participate, or only very sparsely. It did not help much to make the assignment part of the course evaluation. The course received mixed reviews from the students. The students who were not really interested in the subject, or considered it too much work, complained. In last two years we tried to address this problem by introduction of a tight blogging schedule, and peer-reviews. As we report in this paper, this step radically improved the participation rate, and also learning outcomes were higher, however the student’s opinion of these activities was not amended.

Students’ Acceptance of Peer Review

In this paper we investigate the relationship between Multi-Context Systems and Hybrid MKNF Knowledge Bases. Multi-Context Systems provide an effective and modular way to integrate knowledge from different heterogeneous sources (contexts) through so-called bridge rules. Hybrid MKNF Knowledge Bases, based on the logic of minimal knowledge and negation as failure (MKNF), allow for a seamless combination of description logic ontology languages with non-monotonic logic programming rules. In this paper, we not only show that Hybrid MKNF Knowledge Bases can be used as particular contexts in Multi-Context Systems, but we also provide transformations from the former into the latter, without the need for an explicit Hybrid MKNF context, hence providing a way for agents to reason with Hybrid MKNF Knowledge Bases within Multi-Context Systems without the need for specialized Hybrid MKNF reasoners.