Sergio Tessaris

Querying the Semantic Web: A Formal Approach

Ontologies are set to play a key role in the Semantic Web, and several web ontology languages, like DAML+OIL, are based on DLs. These not only provide a clear semantics to the ontology languages, but allows them to exploit DL systems in order to provide correct and complete reasoning services.Recent results shown that DL systems can be enriched by a conjunctive query language, providing a solution to one of the weakness of traditional DL systems. These results can be transfered to the Semantic Web community, where the need for expressive query languages is witnessed by different proposals (like DQL for DAML+OIL).In this paper we present a logical framework for conjunctive query answering in DAML+OIL. Moreover, we provide a sound and complete algorithm based on recent Description Logic research.

An ontology based visual tool for query formulation support

In this paper we describe the principles of the design and development of an intelligent query interface, done in the context of the SEWASIE (SEmantic Webs and AgentS in Integrated Economies) European IST project. The SEWASIE project aims at enabling a uniform access to heterogeneous data sources through an integrated ontology. The query interface is meant to support a user in formulating a precise query - which best captures her/his information needs - even in the case of complete ignorance of the vocabulary of the underlying information system holding the data. The intelligence of the interface is driven by an ontology describing the domain of the data in the information system. The final purpose of the tool is to generate a conjunctive query ready to be executed by some evaluation engine associated to the information system.

How to decide query containment under constraints using a description logic

We present a procedure for deciding (database) query containment under constraints. The technique is to extend the logic DLR with an ABox, and to transform query subsumption problems into DLR ABox satisfiability problems. Such problems can then be decided, via a reification transformation, using a highly optimised reasoner for the SHIQ description logic. We use a simple example to support our hypothesis that this procedure will work well with realistic problems.

Rules and Queries with Ontologies: A Unified Logical Framework

In this paper we present a common framework for investigating the problem of combining ontology and rule languages. The focus of this paper is in the context of Semantic Web (SW), but the approach can be applied in any Description Logics (DL) based system. In the last part, we will show how rules are strictly related to queries.

Automatic Extraction of Ontologies Wrapping Relational Data Sources

Describing relational data sources (i.e. databases) by means of ontologies constitutes the foundation of most of the semantic based approaches to data access and integration. In spite of the importance of the task this is mostly carried out manually and, to the best of our knowledge, not much research has been devoted to its automatisation. In this paper we introduce an automatic procedure for building ontologies starting from the integrity constraints present in the relational sources. Our work builds upon the wide literature on database schema reverse engineering; however, we adapt these techniques to the specific purpose of reusing the extracted schemata (or ontologies) in the context of semantic data access. In particular, we ensure that the underlying data sources can be queried through the ontologies and the extracted ontologies can be used for semantic integration using recently developed techniques in this area. In order to represent the extracted ontology we adopt a variant of the DLR-Lite description logic because of its ability to express the mostly used modelling constraints, and its nice computational properties. The connection with the relational data sources is captured by means of sound views. Moreover, the adoption of this formal language enables us to prove that the extracted ontologies preserve the semantics of the integrity constraints in the relational sources. Therefore, there is no data loss, and the extracted ontology constitutes a faithful wrapper of the relational sources.

On relating heterogeneous elements from different ontologies

In the extensive usage of ontologies envisaged by the Semantic Web there is a compelling need for expressing mappings between different elements of heterogeneous ontologies. State of the art languages for ontology mapping enable to express semantic relations between homogeneous components of different ontologies; namely, they allow to map concepts into concepts, individuals into individuals, and properties into properties. In many real world cases this is not enough; for example when relations in an ontology correspond to a class in another ontology (i.e. reification of relations). To support this kind of interoperability we need therefore richer mapping languages, offering constructs for the representation of heterogeneous mappings. In this paper, we propose an extension of Distributed Description Logics (DDL) with mappings between concepts and relations. We provide a semantics of the proposed extension and sound and complete characterisation of the effects of these mappings in terms of the new ontological knowledge they entail.

The ICOM 3.0 intelligent conceptual modelling tool and methodology

ICOM (version 3.0) is an advanced conceptual modelling tool, which allows the user to design multiple extended ontologies. Each project can be organised into several ontologies, with the possibility to include inter- and intra-ontology constraints. Complete logical reasoning is employed by the tool to verify the specification, infer implicit facts, devise stricter constraints, and manifest any inconsistency. ICOM is fully integrated with a very powerful description logic reasoning server which acts as a background inference engine. The intention behind ICOM is to provide a simple conceptual modelling tool that demonstrates the use of, and stimulates interest in, the novel and powerful knowledge representation based technologies for database and ontology design.

Logical reconstruction of RDF and ontology languages

In this sketchy paper we introduce a logical reconstruction of the RDF family of languages and the OWL-DL family of languages. We prove that our logical framework is equivalent to the standard W3C definitions of RDF and OWL-DL/Lite. The main aim is to have a unified model theoretic semantics for both worlds. As a consequence we get various complexity results and a model theoretic semantics for basic SPARQL.

Reasoning Web. Semantic Technologies for Information Systems

This book contains a collection of seven thoroughly revised tutorial papers based on lectures given by leading researchers at the 5th International Summer School on the Reasoning Web, held in Brixen-Bressanone, Italy, from August 30 to September 4, 2009. The objective of the book is to provide a coherent introduction to semantic web methods and research issues with a particular emphasis on reasoning. The focus of this year s event was on the use of semantic technologies to enhance data access on the web. Topics covered include design and analysis of reasoning procedures for description logics; answer set programming basics, its modeling methodology and its principal extensions tailored for semantic web applications; languages for constraining and querying XML data; RDF database theory and efficient and scalable support for RDF/OWL data storage, loading, inferencing and querying; tractable description logics and their use for ontology-based data access; and the social semantic desktop, which defines a user s personal information environment as a source and end-point of the semantic web

Completing Workflow Traces Using Action Languages

The capability to monitor process and service executions, which has gone to notably increase in the last decades due to the growing adoption of IT-systems, has brought to the diffusion of several reasoning-based tools for the analysis of process executions. Nevertheless, in many real cases, the different degrees of abstraction of models and IT-data, the lack of IT-support on all the steps of the model, as well as information hiding, result in process execution data conveying only incomplete information concerning the process-level activities. This may hamper the capability to analyse and reason about process executions. This paper presents a novel approach to recover missing information about process executions, relying on a reformulation in terms of a planning problem.