On the SPARQL Direct Semantics Entailment Regime for OWL 2 QL

OWL 2 QL is the profile of OWL 2 targeted to Ontology-Based Data Access (OBDA) scenarios, where large amount of data are to be accessed and thus query answering is required to be especially efficient in the size of such data, namely AC0 in data complexity. On the other hand, the syntax and the semantics of the SPARQL query language for OWL 2 is defined by means of the Direct Semantics Entailment Regime (DSER), which considers queries including any assertion expressible in the language of the queried ontology, i.e., both ABox atoms, TBox atoms and inequalities expressed by means of DifferentIndividuals atoms. Thus, in this paper, we investigate query answering over OWL 2 QL under DSER. In particular, we show that, by virtue of the restricted meaning assigned to existential variables and union, query answering can be reduced to the evaluation of a Datalog program. Finally, we investigate query answering under a new SPARQL entailment regime, called Direct Semantics Answering Regime (DSAR), obtained by modifying DSER in such a way that existentially quantified variables are assigned the classical logical meaning, and provide an algorithm for answering queries over OWL 2 QL ontologies under DSAR, that is AC0 in data complexity, for a class of queries comprising both TBox atoms, ABox atoms and inequalities

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

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

Semantic technology for open data publishing

After years of focus on technologies for big data storing and processing, many observers are pointing out that making sense of big data cannot be done without suitable tools for conceptualizing, preparing, and integrating data (see http://www.dbta.com/). Research in the last years has shown that taking into account the semantics of data is crucial for devising powerful data integration solutions. In this work we focus on a specific paradigm for semantic data integration, named "Ontology-Based Data Access" (OBDA), proposed in [1-4]. According to such paradigm, the client of the information system is freed from being aware of how data and processes are structured in concrete resources (databases, software programs, services, etc.), and interacts with the system by expressing her queries and goals in terms of a conceptual representation of the domain of interest, called ontology. More precisely, a system realizing the vision of OBDA is constituted by three components: The ontology, whose goal is to provide a formal, clean and high level representation of the domain of interest, and constitutes the component with which the clients of the system (both humans and software programs) interact. fiedata source layer, representing the existing data sources in the information system, which are managed by the processes and services operating on their data. e mapping between the two layers, which is an explicit representation of the relationship between the data sources and the ontology, and is used to translate the operations on the ontology (e.g., query answering) in terms of concrete actions on the data sources.

Non-Monotonic Ontology-based Abstractions of Data Services

In Ontology-Based Data Access (OBDA), a domain ontology is linked to the data sources of an organization in order to query, integrate and manage data through the concepts and relations of the domain of interest, thus abstracting from the structure and the implementation details of the data layer. While the great majority of contributions in OBDA in the last decade have been concerned with the issue of computing the answers of queries expressed over the ontology, recent papers address a different problem, namely the one of providing suitable abstractions of data services, i.e., characterizing or explaining the semantics of queries over the sources in terms of queries over the domain ontology. Current works on this subject are based on expressing abstractions in terms of unions of conjunctive queries (UCQs). In this paper we advocate the use of a non-monotonic language for this task. As a first contribution, we present a simple extension of UCQs with nonmonotonic features, and show that non-monotonicity provides more expressive power in characterizing the semantics of data services. A second contribution is to prove that, similarly to the case of monotonic abstractions, depending on the expressive power of the languages used to specify the various components of the OBDA system, there are cases where neither perfect nor approximated abstractions exist for a given data service. As a third contribution, we single out interesting special cases where the existence of abstractions is guaranteed, and we present algorithms for computing such abstractions in these cases

Monotone Abstractions in Ontology-Based Data Management

In Ontology-Based Data Management (OBDM), an abstraction of a source query q is a query over the ontology capturing the semantics of q in terms of the concepts and the relations available in the ontology. Since a perfect characterization of a source query may not exist, the notions of best sound and complete approximations of an abstraction have been introduced and studied in the typical OBDM context, i.e., in the case where the ontology is expressed in DL-Lite, and source queries are expressed as unions of conjunctive queries (UCQs). Interestingly, if we restrict our attention to abstractions expressed as UCQs, even best approximations of abstractions are not guaranteed to exist. Thus, a natural question to ask is whether such limitations affect even larger classes of queries. In this paper, we answer this fundamental question for an essential class of queries, namely the class of monotone queries. We define a monotone query language based on disjunctive Datalog enriched with an epistemic operator, and show that its expressive power suffices for expressing the best approximations of monotone abstractions of UCQs

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

Complexity and composition of synthesized web services

The paper investigates fundamental decision problems and composition synthesis for Web services commonly found in practice. We propose a notion of synthesized Web services (SWS’s) to specify the behaviors of the services. Upon receiving a sequence of input messages, an SWS issues multiple queries to a database and generates actions, in parallel; it produces external messages and database updates by synthesizing the actions parallelly generated. In contrast to previous models for Web services, SWS’s advocate parallel processing and (deterministic) synthesis of actions. We classify SWS’s based on what queries an SWS can issue, how the synthesis of actions is expressed, and whether unbounded input sequences are allowed in a single interaction session. We show that the behaviors of Web services supported by various prior models, data-driven or not, can be specified by different SWS classes. For each of these classes we study the non-emptiness, validation and equivalence problems, and establish matching upper and lower bounds on these problems. We also provide complexity bounds on composition synthesis for these SWS classes, identifying decidable cases

Serum osteopontin negatively impacts on intima-media thickness in patients with systemic lupus erythematosus

BACKGROUND Ultrasound evaluation of carotid intima-media thickness (cIMT) has been extensively used for potentially improving cardiovascular (CV) risk stratification in several patients' categories. Subjects with systemic lupus erythematosus (SLE) have been investigated by both imaging and molecular biomarker approaches with contrasting results. Here, we focused on the role of osteopontin (OPN) as biomarker of subclinical atherosclerosis associated with SLE. MATERIALS AND METHODS Eighty females (age 18-65 years) affected by SLE and eighty age-matched healthy female controls without a clinical history of CV disease underwent ultrasound evaluation of cIMT and blood sample assay of high-sensitivity C-reactive protein (hs-CRP) and OPN. RESULTS Healthy controls and SLE patients significantly differed for CV risk factors (ie, waist circumference, hypertension and dyslipidaemia) and the inflammatory status. Noteworthy, an opposite association between cIMT and OPN was observed in the two study groups. Whereas OPN was positively associated with mean cIMT (r = 0.364; P = 0.001) in SLE patients, a negative correlation was found in healthy controls. Furthermore, in SLE patients increased circulating levels of OPN were associated with the use of hydroxychloroquine and the positivity for the anti-dsDNA autoantibodies. At linear regression analysis, only OPN remained independently associated with cIMT also after adjustment for age, smoking pack-year, Heart SCORE, disease length and steroid therapy length. CONCLUSIONS These results indicate that serum OPN levels were strongly associated with subclinical atherosclerosis in patients with LES and it might be a useful CV biomarker that requires additional validation in larger trials