A Higher-Order Semantics for Metaquerying in OWL 2 QL

Inspired by recent work on higher-order Description Logics, we propose HOS, a new semantics for OWL 2 QL ontologies. We then consider SPARQL queries which are legal under the direct semantics entailment regime, we extend them with logical union, existential variables, and unrestricted use of variables so as to express meaningful meta-level queries. We show that both satisfiability checking and answering instance queries with metavariables have the same ABox complexity as under direct semantic

Using Ontologies for Semantic Data Integration

While big data analytics is considered as one of the most important paths to competitive advantage of today’s enterprises, data scientists spend a comparatively large amount of time in the data preparation and data integration phase of a big data project. This shows that data integration is still a major challenge in IT applications. Over the past two decades, the idea of using semantics for data integration has become increasingly crucial, and has received much attention in the AI, database, web, and data mining communities. Here, we focus on a specific paradigm for semantic data integration, called Ontology-Based Data Access (OBDA). The goal of this paper is to provide an overview of OBDA, pointing out both the techniques that are at the basis of the paradigm, and the main challenges that remain to be addressed

Metamodeling and metaquerying in OWL 2 QL

OWL 2 QL is a standard profile of the OWL 2 ontology language, specifically tailored to Ontology-Based Data Management. Inspired by recent work on higher-order Description Logics, in this paper we present a new semantics for OWL 2 QL ontologies, called Metamodeling Semantics (MS), and show that, in contrast to the official Direct Semantics (DS) for OWL 2, it allows exploiting the metamodeling capabilities natively offered by the OWL 2 punning. We then extend unions of conjunctive queries with both metavariables, and the possibility of using TBox atoms, with the purpose of expressing meaningful metalevel queries. We first show that under MS both satisfiability checking and answering queries including only ABox atoms, have the same complexity as under DS. Second, we investigate the problem of answering general metaqueries, and single out a new source of complexity coming from the combined presence of a specific type of incompleteness in the ontology, and of TBox axioms among the query atoms. Then we focus on a specific class of ontologies, called TBox-complete, where there is no incompleteness in the TBox axioms, and show that general metaquery answering in this case has again the same complexity as under DS. Finally, we move to general ontologies and show that answering general metaqueries is coNP-complete with respect to ontology complexity, Π2p-complete with respect to combined complexity, and remains AC0 with respect to ABox complexity

Answering metaqueries over Hi(OWL 2 QL) ontologies

Hi(OWL 2 QL) is a new ontology language with the OWL2QL syntax and a specific semantics designed to support metamodeling and metaquerying. In this paper we investigate the problem of answering metaqueries in Hi(OWL 2 QL), which are unions of conjunctive queries with both ABox and TBox atoms. We first focus on a specific class of ontologies, called TBox-complete, where there is no uncertainty about TBox axioms, and show that query answering in this case has the same complexity (both data and combined) as in OWL 2 QL. We then move to general ontologies and show that answering metaqueries is coNP-complete with respect to ontology complexity, Π2p-complete with respect to combined complexity, and remains AC0 with respect to ABox complexity. Finally, we present an optimized query answering algorithm that can be used for TBox-complete ontologies

Design and foundations of ontologies with meta-modelling.

Ontologies are broadly used and proved modelling artifacts to conceptualize a domain. In particular the W3C standard ontology language OWL, based on description logics, allows the ontology engineer to formally represent a domain as a set of assertions about concepts, individuals and roles. Nowadays, complex applications leads to combine autonomously built ontologies into ontology networks by relating them through di erent kind of relations. Some relations, such as the mapping of two concepts from di erent ontologies, can be expressed by the standard ontology language OWL, i.e. by the description logics behind it. However, there are other kind of relations that are not soundly represented by OWL, such as the meta-modelling relation. The meta-modelling relation has to do with the modelling of the same real object with di erent abstraction levels, e.g. as a concept in one ontology and as an individual in another ontology. Even though there are a set of approaches that extend description logics to deal with meta-modelling, they do not solve relevant requirements of some real scenarios. The present thesis work introduces an extension to the description logic SHIQ which provides a exible syntax and a strong semantics, and moreover ensures the well-foundedness of the interpretation domain. This approach is di erent from existing meta-modelling approaches either in the syntax or in the semantics (or both), and moreover ensures the well-foundedness of the domain which is an original contribution from the theoretical point of view. The meta-modelling extension of SHIQ introduced in the present work is justi ed by a detailed description of a set of real case studies, with an analysis of the bene ts of the new approach to solve some relevant requirements. Finally, the present work addresses the methodological issue by introducing a design pattern to help the ontology engineer in the use of the proposed meta-modelling approach