The Experts below are selected from a list of 5457 Experts worldwide ranked by ideXlab platform
Giorgos Stamou - One of the best experts on this subject based on the ideXlab platform.
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Query Extensions and Incremental Query Rewriting for OWL 2 QL Ontologies
Journal on Data Semantics, 2014Co-Authors: Tassos Venetis, Giorgos Stoilos, Giorgos StamouAbstract:Query Rewriting over lightweight ontologies, like DL-Lite ontologies, is a prominent approach for ontology-based data access. It is often the case in realistic scenarios that users ask an initial Query which they later refine, e.g., by extending it with new constraints making their initial request more precise. So far, all DL-Lite systems would need to process the new Query from scratch. In this paper, we study the problem of computing the Rewriting of an extended Query by ‘extending’ a previously computed Rewriting of the initial Query and avoiding recomputation. Interestingly, our approach also implies a novel algorithm for computing the Rewriting of a fixed Query. More precisely, the Query can be ‘decomposed’ into its atoms and then each atom can be processed incrementally. We present detailed algorithms, several optimisations for improving the performance of our Query Rewriting algorithm, and finally, an experimental evaluation.
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optimized Query Rewriting for owl 2 ql
Conference on Automated Deduction, 2011Co-Authors: Alexandros Chortaras, Despoina Trivela, Giorgos StamouAbstract:The OWL 2 QL profile has been designed to facilitate Query answering via Query Rewriting. This paper presents an optimized Query Rewriting algorithm which takes advantage of the special characteristics of the Query Rewriting problem via first-order resolution in OWL 2 QL and computes efficiently the Rewriting set of a user Query, by avoiding blind and unnecessary inferences, as well as by reducing the need for extended subsumption checks. The evaluation shows that in several cases the algorithm achieves a significant improvement and better practical scalability if compared to other similar approaches.
Riccardo Rosati - One of the best experts on this subject based on the ideXlab platform.
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kyrie2 Query Rewriting under extensional constraints in elhio
International Semantic Web Conference, 2014Co-Authors: Jose Mora, Riccardo Rosati, Oscar CorchoAbstract:In this paper we study Query answering and Rewriting in ontologybased data access. Specifically, we present an algorithm for computing a perfect Rewriting of unions of conjunctive queries posed over ontologies expressed in the description logic ELHIO, which covers the OWL 2 QL and OWL 2 EL profiles. The novelty of our algorithm is the use of a set of ABox dependencies, which are compiled into a so-called EBox, to limit the expansion of the Rewriting. So far, EBoxes have only been used in Query Rewriting in the case of DL-Lite, which is less expressive than ELHIO. We have extensively evaluated our new Query Rewriting technique, and in this paper we discuss the tradeoff between the reduction of the size of the Rewriting and the computational cost of our approach.
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optimizing Query Rewriting in ontology based data access
Extending Database Technology, 2013Co-Authors: Floriana Di Pinto, Riccardo Rosati, Domenico Lembo, Maurizio Lenzerini, Riccardo Mancini, Antonella Poggi, Marco Ruzzi, Domenico Fabio SavoAbstract:In ontology-based data access (OBDA), an ontology is connected to autonomous, and generally pre-existing, data repositories through mappings, so as to provide a high-level, conceptual view over such data. User queries are posed over the ontology, and answers are computed by reasoning both on the ontology and the mappings. Query answering in OBDA systems is typically performed through a Query Rewriting approach which is divided into two steps: (i) the Query is rewritten with respect to the ontology (ontology Rewriting of the Query); (ii) the Query thus obtained is then reformulated over the database schema using the mapping assertions (mapping Rewriting of the Query). In this paper we present a new approach to the optimization of Query Rewriting in OBDA. The key ideas of our approach are the usage of inclusion between mapping views and the usage of perfect mappings, which allow us to drastically lower the combinatorial explosion due to mapping Rewriting. These ideas are formalized in PerfectMap, an algorithm for OBDA Query Rewriting. We have experimented PerfectMap in a real-world OBDA scenario: our experimental results clearly show that, in such a scenario, the optimizations of PerfectMap are crucial to effectively perform Query answering.
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prexto Query Rewriting under extensional constraints in dl lite
International Semantic Web Conference, 2012Co-Authors: Riccardo RosatiAbstract:In this paper we present Prexto, an algorithm for computing a perfect Rewriting of unions of conjunctive queries over ontologies expressed in the description logic DL−Lite. The main novelty of Prexto lies in the fact that it constitutes the first technique for Query Rewriting over ontologies which fully exploits extensional constraints to optimize Query Rewriting. In addition, Prexto makes use of functional role axioms and of concept and role disjointness axioms to optimize the size of the rewritten Query. We show that these optimizations allow Prexto to outperform the existing Query Rewriting techniques for DL−Lite in practical cases.
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Query Rewriting for inconsistent dl lite ontologies
Web Reasoning and Rule Systems, 2011Co-Authors: Domenico Lembo, Riccardo Rosati, Maurizio Lenzerini, Marco Ruzzi, Domenico Fabio SavoAbstract:In this paper we study the problem of obtaining meaningful answers to queries posed over inconsistent DL-Lite ontologies. We consider different variants of inconsistency-tolerant semantics and show that for some of such variants answering unions of conjunctive queries (UCQs) is first-order (FOL) rewritable, i.e., it can be reduced to standard evaluation of a FOL/SQL Query over a database. Since FOL-rewritability of Query answering for UCQs over consistent ontologies under first-order logic semantics is one of the distinguishing features of DL-Lite, in this paper we actually identify some settings in which such property is preserved also under inconsistency-tolerant semantics. We therefore show that in such settings inconsistency-tolerant Query answering has the same computational complexity of standard Query answering and that it can rely on well-established relational database technology, as under standard DL semantics.
Mahmoud Barhamgi - One of the best experts on this subject based on the ideXlab platform.
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Privacy Query Rewriting algorithm instrumented by a privacy-aware access control model
Annals of Telecommunications - annales des télécommunications, 2013Co-Authors: Said Oulmakhzoune, Mahmoud Barhamgi, Nora Cuppens-boulahia, Frédéric Cuppens, Stéphane Morucci, Djamal BenslimaneAbstract:In this paper we present an approach to instrument a SPARQL Query Rewriting algorithm enforcing privacy preferences. The term instrument is used to mean supplying appropriate constraints. We show how to design a real and effective instrumentation process of a Rewriting algorithm using an existing privacy aware access control model like PrivOrBAC. We take into account various dimensions of privacy preferences through the concepts of consent, accuracy, purpose and recipient. We implement and evaluate our process of privacy enforcement based on a healthcare scenario.
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Electronic Health Record Data-as-a-Services Composition Based on Query Rewriting
Transactions on Large-Scale Data- and Knowledge-Centered Systems, 2011Co-Authors: Idir Amine Amarouche, Mahmoud Barhamgi, Djamal Benslimane, Michael Mrissa, Zaia AlimazighiAbstract:Due to the large development of medical information systems over the last few years, there is today a strong need for an infrastructure that uniformly integrates the distributed and heterogeneous collections of patient data to deliver value-added information to healthcare professionals at the points of care. The adoption of Electronic Health Records (EHRs) and Web services as a software infrastructure has become an extremely important prerequisite for patient data integration. In this paper we propose a semantic-enabled architecture for the automatic composition of EHR (Electronic Health Record) DaaSs (Data-as-a-Service). In our architecture, DaaSs are selected and composed automatically to resolve the user queries (i.e. queries posed by physicians, nurses, etc) using a Query Rewriting approach. Our proposed approach can also handle the semantic conflicts of data exchanged among component services in an EHR DaaS composition by deriving and applying automatically the necessary data conversions.
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a Query Rewriting approach for web service composition
IEEE Transactions on Services Computing, 2010Co-Authors: Mahmoud Barhamgi, Djamal Benslimane, Brahim MedjahedAbstract:Data-Providing (DP) services allow Query-like access to organizations' data via web services. The invocation of a DP service results in the execution of a Query over data sources. In most cases, users' queries require the composition of several services. In this paper, we propose a novel approach for Querying and automatically composing DP services. The proposed approach largely draws from the experiences and lessons learned in the areas of service composition, ontology, and answering queries over views. First, we introduce a model for the description of DP services and specification of service-oriented queries. We model DP services as RDF views over a mediated (domain) ontology. Each RDF view contains concepts and relations from the mediated ontology to capture the semantic relationships between input and output parameters. Second, we propose Query Rewriting algorithms for processing queries over DP services. The Query mediator automatically transforms a user's Query (during the Query Rewriting stage) into a composition of DP services. Finally, we describe an implementation and provide a performance evaluation of the proposed approach.
Brahim Medjahed - One of the best experts on this subject based on the ideXlab platform.
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a Query Rewriting approach for web service composition
IEEE Transactions on Services Computing, 2010Co-Authors: Mahmoud Barhamgi, Djamal Benslimane, Brahim MedjahedAbstract:Data-Providing (DP) services allow Query-like access to organizations' data via web services. The invocation of a DP service results in the execution of a Query over data sources. In most cases, users' queries require the composition of several services. In this paper, we propose a novel approach for Querying and automatically composing DP services. The proposed approach largely draws from the experiences and lessons learned in the areas of service composition, ontology, and answering queries over views. First, we introduce a model for the description of DP services and specification of service-oriented queries. We model DP services as RDF views over a mediated (domain) ontology. Each RDF view contains concepts and relations from the mediated ontology to capture the semantic relationships between input and output parameters. Second, we propose Query Rewriting algorithms for processing queries over DP services. The Query mediator automatically transforms a user's Query (during the Query Rewriting stage) into a composition of DP services. Finally, we describe an implementation and provide a performance evaluation of the proposed approach.
Oscar Corcho - One of the best experts on this subject based on the ideXlab platform.
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Query Rewriting in rdf stream processing
International Semantic Web Conference, 2016Co-Authors: Jeanpaul Calbimonte, Jose Mora, Oscar CorchoAbstract:Querying and reasoning over RDF streams are two increasingly relevant areas in the broader scope of processing structured data on the Web. While RDF Stream Processing RSP has focused so far on extending SPARQL for continuous Query and event processing, stream reasoning has concentrated on ontology evolution and incremental materialization. In this paper we propose a different approach for Querying RDF streams over ontologies, based on the combination of Query Rewriting and stream processing. We show that it is possible to rewrite continuous queries over streams of RDF data, while maintaining efficiency for a wide range of scenarios. We provide a detailed description of our approach, as well as an implementation, StreamQR, which is based on the kyrie rewriter, and can be coupled with a native RSP engine, namely CQELS. Finally, we show empirical evidence of the performance of StreamQR in a series of experiments based on the SRBench Query set.
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kyrie2 Query Rewriting under extensional constraints in elhio
International Semantic Web Conference, 2014Co-Authors: Jose Mora, Riccardo Rosati, Oscar CorchoAbstract:In this paper we study Query answering and Rewriting in ontologybased data access. Specifically, we present an algorithm for computing a perfect Rewriting of unions of conjunctive queries posed over ontologies expressed in the description logic ELHIO, which covers the OWL 2 QL and OWL 2 EL profiles. The novelty of our algorithm is the use of a set of ABox dependencies, which are compiled into a so-called EBox, to limit the expansion of the Rewriting. So far, EBoxes have only been used in Query Rewriting in the case of DL-Lite, which is less expressive than ELHIO. We have extensively evaluated our new Query Rewriting technique, and in this paper we discuss the tradeoff between the reduction of the size of the Rewriting and the computational cost of our approach.
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towards a systematic benchmarking of ontology based Query Rewriting systems
International Semantic Web Conference, 2013Co-Authors: Jose Mora, Oscar CorchoAbstract:Query Rewriting is one of the fundamental steps in ontology-based data access (OBDA) approaches. It takes as inputs an ontology and a Query written according to that ontology, and produces as an output a set of queries that should be evaluated to account for the inferences that should be considered for that Query and ontology. Different Query Rewriting systems give support to different ontology languages with varying expressiveness, and the rewritten queries obtained as an output do also vary in expressiveness. This heterogeneity has traditionally made it difficult to compare different approaches, and the area lacks in general commonly agreed benchmarks that could be used not only for such comparisons but also for improving OBDA support. In this paper we compile data, dimensions and measurements that have been used to evaluate some of the most recent systems, we analyse and characterise these assets, and provide a unified set of them that could be used as a starting point towards a more systematic benchmarking process for such systems. Finally, we apply this initial benchmark with some of the most relevant OBDA approaches in the state of the art.
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engineering optimisations in Query Rewriting for obda
International Conference on Semantic Systems, 2013Co-Authors: Jose Mora, Oscar CorchoAbstract:Ontology-based data access (OBDA) systems use ontologies to provide views over relational databases. Most of these systems work with ontologies implemented in description logic families of reduced expressiveness, what allows applying efficient Query Rewriting techniques for Query answering. In this paper we describe a set of optimisations that are applicable with one of the most expressive families used in this context (ELHIO). Our resulting system exhibits a behaviour that is comparable to the one shown by systems that handle less expressive logics.
