Citation Context

... 17]. In Section 5, we present a simple approach for querying RDFS data that was proposed in [18, 29, 34]. Dealing with queries that consider the OWL semantics is a very interesting topic of research =-=[39, 17, 25]-=-, but it is out of the scope of this paper. Navigating RDF graphs: As with any data model, a natural question is what are the desired features for an RDF query language. Among the multiple design issu...

Citation Context

...nd large-scale datasets. Some OWL 2 reasoners, such as HermiT, Pellet and RACER, support query answering, but despite intensive efforts at optimisation they can only deal with modestly-sized datasets =-=[14,15,10]-=-. The idea of using a rule-based engine for query answering over ontologies in the description logic SHIQ was proposed by Hustadt et al. [11] and implemented in the KAON2 system. The transformation of...

Citation Context

... (Hustadt et al. 2004). Concerning ontologies, we observe that the field of ontology-based Query Answering (QA) is thriving in data and knowledge management (Calvanese et al. 2007; Cal̀ı et al. 2009; =-=Kollia et al. 2011-=-; Cal̀ı et al. 2011), and companies such as Oracle are adding ontological reasoning modules on top of their existing software. In this context, queries are not merely evaluated on an extensional relat...

Citation Context

...logy. 15 http://www.optique-project.eu/ 16 http://dblp.uni-trier.de/xml/ 10.2 Query Evaluation Engine The evaluation engine considered is an extension of the OWL 2 reasoner HermiT, known as OWL-BGP17 =-=[22]-=-. OWL-BGP is able to process SPARQL queries in the SPARQLOWL fragment, under the OWL 2 Direct Semantics entailment regime [22]. The queries employed in the OA4QA track are standard conjunctive queries...

Citation Context

...dard queries, but that the proposed optimizations can dramatically improve performance, in some cases by as much as three orders of magnitude. An extended version of this paper is accepted at ESWC’11 =-=[10]-=-. 2 Preliminaries In this section we give a brief introduction to the SPARQL-OWL entailment regime and in the next section we describe an algorithm that finds answers to queries under this regime. 2.1...

Citation Context

... generating candidates for concept atoms, such that approximation techniques (to, e.g., DL-Lite) are not required in many cases. We demonstrate our findings using the LUBM benchmark as done, e.g., in =-=[9]-=- and [6]. As an additional extension to Wandelt’s work, which uses specific storage layouts for storing Abox data descriptions and internal information in SQL databases, we investigate ontologybased a...

Citation Context

...es of individuals, which are instances of the queried classes and properties. Such BGPs are first mapped to OWL class and (object) property assertions that allow for variables in place of individuals =-=[7]-=-. For brevity, we directly write mapped BGPs in DL syntax extended to allow for variables. We use the term query in the remainder for such BGPs. W.l.o.g., we assume that queries are connected [2]. Def...

Citation Context

... due to the lack of space, we do not cover in this section other important features of SPARQL 1.1 like the use of aggregates and negation, and the inclusion in the language of some entailment regimes =-=[17, 30]-=- to deal with the RDFS [26] and OWL [38, 28] vocabularies. 2.2.1 Federation Since the release of SPARQL 1.0 in 2008, the Web has witnessed a constant growth in the amount of RDF data publicly availabl...

Citation Context

...which shows that it can lead to an improvement of up to two orders of magnitude in the execution times of some queries. The polarity based optimisation can be found in more detail in our earlier work =-=[11]-=-. 2 Preliminaries Due to lack of space, we do not introduce the Description Logic SHIQ, which we use throughout the paper. For further details, we refer interested readers to the DL handbook [1]. We a...

Citation Context

... according to the RDFS regime. – HermiT [22] (version 1.3.6) is a DL reasoner based on hypertableau calculus [15]. It can be used to answer sparql1.0 queries by means of the sparql1.0 wrapper owl-bgp =-=[10,13]-=-. For the sake of simplicity, in the following we will mention the composition between the reasoner and the wrapper simply as “HermiT”. – kaon2 [12,14] (version 2008-06-29) implements reasoning algori...