Evgenij Thorstensen

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The Partner Units Problem is a specific type of configuration problem with important applications in the area of surveillance and security. In this work we show that a special case of the problem, that is of great interest to our partners in industry, can directly be tackled via a structural problem decompostion method. Combining these theoretical insights(More)
This paper reviews structural problem decomposition methods, such as tree and path decompositions. It is argued that these notions can be applied in two distinct ways: Either to show that a problem is efficiently solvable when a width parameter is fixed, or to prove that the unrestricted (or some width-parameter free) version of a problem is tractable by(More)
Ontology Based Data Access (OBDA) is a prominent approach to query databases which uses an ontology to expose data in a conceptually clear manner by abstracting away from the technical schema-level details of the underlying data. The ontology is ‘connected’ to the data via mappings that allow to automatically translate queries posed over the ontology into(More)
In this work we present the Partner Units Problem as a novel challenge for optimization methods. It captures a certain type of configuration problem that frequently occurs in industry. Unfortunately, it can be shown that in the most general case an optimization version of the problem is intractable. We present and evaluate encodings of the problem in the(More)
Ontologies have recently became a popular mechanism to expose relational database (RDBs) due to their ability to describe the domain of data in terms of classes and properties that are clear to domain experts. Ontological terms are related to the schema of the underlying databases with the help of mappings, i.e., declarative specifications associating SQL(More)
Ontology-based data access (OBDA) is a recent paradigm for accessing data sources through an ontology that acts as a conceptual, integrated view of the data, and declarative mappings that connect the ontology to the data sources. We study the formal analysis of mappings in OBDA. Specifically, we focus on the problem of identifying mapping inconsistency and(More)
The Optique project aims at developing an end-to-end system for semantic data access to Big Data in industries such as Statoil ASA and Siemens AG. In our demonstration we present the first version of the Optique system customised for the Norwegian Petroleum Directorate’s FactPages, a publicly available dataset relevant for engineers at Statoil ASA. The(More)
In this paper we study mapping analysis in ontology-based data access (OBDA), providing an initial set of foundational results for this problem. We start by defining general, language-independent notions of mapping inconsistency, mapping subsumption, and mapping redundancy in OBDA. Then, we focus on specific mapping languages for OBDA and illustrate(More)
In this demo paper we present BOOTOX, a system facilitating ontology and mapping development by their automatic extraction (i.e., bootstrapping) from relational databases. BOOTOX has a number of advantages: it allows to control the OWL 2 profile of the output ontologies, and to bootstrap complex and provenance mappings, which are beyond the W3C direct(More)
Instance-based methods are a specific class of methods for automated proof search in first-order logic. This article provides an overview of the major methods in the area and discusses their properties and relations to the more established resolution methods. It also discusses some recent trends on refinements and applications. This overview is rather brief(More)