1,720,976 research outputs found
LOM: a linguistic ontology matcher based on information retrieval
No full textOntology mapping is a key problem to be solved for the success of the Semantic Web and related technologies. An ontology mapping algorithm aims at finding correspondences (or mappings) between entities of the source and target ontologies by combining several matching components, i.e., individual matchers, that exploit one or more sources of information encoded within the ontologies. In this paper, we investigate linguistic techniques for ontology mapping and underline their importance in paving the way to other matching techniques. We define a general mapping model architecture and discuss an implementation in the Lucene ontology matcher (LOM). LOM leverages the features of the Lucene search engine library. The basic idea is to gather the different kinds of linguistic information of the source ontology entities in Lucene documents that will be stored into an index. Mappings are discovered by using the values of entities in the target ontology as search arguments against the index created from the source ontology. Extensive experimental results using a popular benchmark test suite show the effectiveness of this approach in terms of precision, recall, F-measure and execution time as compared to other linguistic approaches
Gize: A time warp in the web of data
No full textWe introduce the Gize framework for querying historical RDF data. Gize builds upon two main pillars: a lightweight approach to keep historical data, and an extension of SPARQL called SPARQ-LTL, which incorporates temporal logic primitives to enable a rich class of queries. One striking point of Gize is that its features can be readily made available in existing query processors
The map generator tool
No full textWe present the MaGe system, which helps users and developers to build maps of the Web graph. Maps abstract and represent in a concise and machine-readable way regions of information on the Web
An algorithm for discovering ontology mappings in P2P systems
No full textOntology Mapping is mandatory for enabling semantic interoperability among different agents and services making use of different ontologies. The ontology mapping problem becomes more critical in P2P systems since: (i) the number of different ontologies can dramatically increase; (ii) ontology mapping must be performed on the fly and only on parts of ontologies contextual to a specific interaction in which the peers are involved; (iii) complex mapping strategies (e.g., structural mapping) cannot be exploited since peers are not aware of one another's ontologies. Hence, specific techniques have to be designed. This paper presents and evaluate the SEmantiC COordinator (SECCO) ontology mapping algorithm that addresses the abovementioned issues by adopting a mapping strategy based on the evaluation of three different similarity measures: syntactic, lexical and contextual. © 2008 Springer-Verlag Berlin Heidelberg
Extended Property Paths: Writing more SPARQL queries in a succinct way
No full textWe introduce Extended Property Paths (EPPs), a significant enhancement of SPARQL property paths. EPPs allow to capture in a succinct way a larger class of navigational queries than property paths. We present the syntax and formal semantics of EPPs and introduce two different evaluation strategies. The first is based on an algorithm implemented in a custom query processor. The second strategy leverages a translation algorithm of EPPs into SPARQL queries that can be executed on existing SPARQL processors. We compare the two evaluation strategies on real data to highlight their pros and cons
A DHT-based semantic overlay network for service discovery
No full textThe number of available Internet services increases every clay. This trend demands distributed models and architectures to support scalability as well as semantics to enable efficient publication and retrieval of services. Two common approaches toward this goal are semantic overlay networks (SONs) and distributed hash tables (DHTs) with semantic extensions. SONs enable semantic-driven query answering but are less scalable than DHTs, which, in their turn, feature efficient but semantic-free query answering based on exact match. This paper presents a strategy and a system, called ERGOT, that combine DHTs and SONs to enable semantic-based service discovery in distributed infrastructures such as Grids and Clouds. ERGOT uses semantic annotations that enrich service specifications in two ways: (i) services are advertised in the DHT on the basis of their annotations, thus allowing us to establish a SON between service providers; (ii) annotations enable semantic-based service matchmaking, using a similarity measure between service requests and descriptions. An extensive evaluation of the system is presented and discussed. The experimental evaluation we carried out confirmed the efficiency of the implemented strategy in terms of both accuracy of search and network traffic. (C) 2011 Elsevier B.V. All rights reserved
Explaining and suggesting relatedness in knowledge graphs
No full textKnowledge graphs (KGs) are a key ingredient for searching, browsing and knowledge discovery activities. Motivated by the need to harness knowledge available in a variety of KGs, we face the following two problems. First, given a pair of entities defined in some KG, find an explanation of their relatedness. We formalize the notion of relatedness explanation and introduce different criteria to build explanations based on information-theory, diversity and their combinations. Second, given a pair of entities, find other (pairs of) entities sharing a similar relatedness perspective. We describe an implementation of our ideas in a tool, called RECAP, which is based on RDF and SPARQL. We provide an evaluation of RECAP and a comparison with related systems on real-world data
The logic of extensional RDFS (Extended abstract)
No full textThe normative version of RDFS gives non-standard (intensional) interpretations to some standard notions such as classes and properties. In this paper we develop the extensional semantics for the RDFS vocabulary, which surprisingly preserves the simplicity and computational complexity of deduction of the intensional case. This result will impact current implementations in a positive sense, as reasoning in RDFS will follow common set-based intuitions and be compatible with OWL extensions; moreover, the rule system that we present is easily embeddable in existing libraries such as Jena
SECCO: On Building Semantic Links in Peer-to-Peer Networks
No full textOntology Mapping is a mandatory requirement for enabling semantic interoperability among different agents and services relying on different ontologies. This aspect becomes more critical in Peer-to-Peer (P2P) networks for several reasons: (i) the number of different ontologies can dramatically increase; (ii) mappings among peer ontologies have to be discovered on the fly and only on the parts of ontologies ``contextual'' to a specific interaction in which peers are involved; (iii) complex mapping strategies (e.g., structural mapping based on graph matching) cannot be exploited since peers are not aware of one another's ontologies. In order to address these issues, we developed a new ontology mapping algorithm called Semantic Coordinator (SECCO). SECCO is composed by three individual matchers: syntactic, lexical and contextual. The syntactic matcher, in order to discover mappings, exploits different kinds of linguistic information (e.g., comments, labels) encoded in ontology entities. The lexical matcher enables discovering mappings in a semantic way since it ``interprets'' the semantic meaning of concepts to be compared. The contextual matcher relies on a ``how it fits'' strategy, inspired by the contextual theory of meaning, and by taking into account the contexts in which the concepts to be compared are used refines similarity values. We show through experimental results that SECCO fulfills two important requirements: fastness and accuracy (i.e., quality of mappings). SECCO, differently from other semantic P2P applications (e.g., Piazza, GridVine) that assume the preexistence of mappings for achieving semantic interoperability, focuses on the problem of finding mappings. Therefore, if coupled with a P2P platform, it paves the way towards a comprehensive semantic P2P solution for content sharing and retrieval, semantic query answering and query routing. We report on the advantages of integrating SECCO in the K-link+ system
Explaining graph navigational queries
No full textGraph navigational languages allow to specify pairs of nodes in a graph subject to the existence of paths satisfying a certain regular expression. Under this evaluation semantics, connectivity information in terms of intermediate nodes/edges that contributed to the answer is lost. The goal of this paper is to introduce the GeL language, which provides query evaluation semantics able to also capture connectivity information and output graphs. We show how this is useful to produce query explanations. We present efficient algorithms to produce explanations and discuss their complexity. GeL machineries are made available into existing SPARQL processors thanks to a translation from GeL queries into CONSTRUCT SPARQL queries. We outline examples of explanations obtained with a tool implementing our framework and report on an experimental evaluation that investigates the overhead of producing explanations
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