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Property:Has abstract
This is a property of type Text.
Pages using the property "Has abstract"
Showing 16 pages using this property.
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| Optimizing SPARQL Queries over Disparate RDF Data Sources through Distributed Semi-joins + | With the ever-increasing amount of data on the Web available at SPARQL endpoints the need for an integrated and transparent way of accessing the data has arisen. It is highly desirable to have a way of asking SPARQL queries that make use of data residing in disparate data sources served by multiple SPARQL endpoints. We aim at providing such a capability and thus enabling an integrated way of querying the whole Semantic Web at a time. + |
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| Querying Distributed RDF Data Sources with SPARQL + | DARQ provides transparent query access to multiple SPARQL services, i.e., it gives the user the impression to query one single RDF graph despite the real data being distributed on the web. A service description language enables the query engine to decompose a query into sub-queries, each of which can be answered by an individual service. DARQ also uses query rewriting and cost-based query optimization to speed-up query execution. + |
| Querying over Federated SPARQL Endpoints : A State of the Art Survey + | The increasing amount of Linked Data and its inherent distributed nature have attracted significant attention throughout the research community and amongst practitioners to search data, in the past years. Inspired by research results from traditional distributed databases, different approaches for managing federation over SPARQL Endpoints have been introduced. SPARQL is the standardised query language for RDF, the default data model used in Linked Data deployments and SPARQL Endpoints are a popular access mechanism provided by many Linked Open Data (LOD) repositories. In this paper, we initially give an overview of the federation framework infrastructure and then proceed with a comparison of existing SPARQL federation frameworks. Finally, we highlight shortcomings in existing frameworks, which we hope helps spawning new research directions. + |
| Querying the Web of Data with Graph Theory-based Techniques + | The increasing amount of Linked Data on the Web enables users to retrieve quality and complex information and to deploy innovative, added-value applications. The volume of available Linked Data and their spread across a large number of repositories make a strong case for ecient distributed SPARQL queries. However, in practice, current distributed SPARQL query processing techniques face issues on performance and scalability. In our previous work we provided initial evidence that graph theory-based techniques can address performance issues better than other approaches such as DARQ. Here we further exploit the potential of graph algorithms and we show how they can address performance and scalability for distributed SPARQL queries even better. To that end, we present an improved engine called GDS and we evaluate it by providing a detailed comparison to existing approaches for distributed queries (i.e. DARQ and FedX). By analyzing the evaluation results, we try to identify promising techniques for distributed SPARQL processing, and to outline the problems that need to be addressed in future research. + |
| Querying the Web of Interlinked Datasets using VOID Descriptions + | Query processing is an important way of accessing data on the Semantic Web. Today, the Semantic Web is characterized as a web of interlinked datasets, and thus querying the web can be seen as dataset integration on the web. Also, this dataset integration must be transparent from the data consumer as if she is querying the whole web. To decide which datasets should be selected and integrated for a query, one requires a metadata of the web of data. In this paper, to enable this transparency, we introduce a federated query engine called WoDQA (Web of Data Query Analyzer) which discovers datasets relevant with a query in an automated manner using VOID documents as metadata. WoDQA focuses on powerful dataset elimination by analyzing query structure with respect to the metadata of datasets. Dataset and linkset descriptions in VOID documents are analyzed for a SPARQL query and a federated query is constructed. By means of linkset concept of VOID, links between datasets are incorporated into selection of federated data sources. Current version ofWoDQA is available as a SPARQL endpoint. + |
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| RDB2ONT: A Tool for Generating OWL Ontologies From Relational Database Systems + | This paper describes a framework that uses the Semantic Web infrastructure to address semantic interoperability between relational database systems in large-scale environments and at multiple levels of granularities. Given a relational database system, we describe a formal algorithm to use the relational database Rs meta-data and structural constraints to construct its OWL ontology while preserving the structural constraints of the underlying relational database system. The generated ontology is described using and conforming to a set of vocabularies defined in an ontology that describes relational database systems on the web. Using this set of vocabularies guarantee that applications on the web can work with data instances that conformed to a set of known vocabularies and structures. Finally, we describe our prototype and how semantic conflicts are resolved between multiple relational database systems using the generated ontologies. + |
| Relational.OWL - A Data and Schema Representation Format Based on OWL + | One of the research fields which has recently gained much scientific interest within the database community are Peer-to-Peer databases, where peers have the autonomy to decide whether to join or to leave an information sharing environment at any time. Such volatile data nodes may appear shortly, collect or deliver some data, and disappear again. It even can not be assured that a peer joins the network ever again. In this paper we introduce a representation format fort both, schema and data information based on the Web Ontology Language OWL. According to the advantages of the Semantic Web we are thus able to represent and to transfer every schema and data component of a database to any partner, without having to define a data and schema exchange format explicitly. + |
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| SERIMI – Resource Description Similarity, RDF Instance Matching and Interlinking + | The interlinking of datasets published in the Linked Data Cloud is a challenging problem and a key factor for the success of the Semantic Web. Manual rule-based methods are the most effective solution for the problem, but they require skilled human data publishers going through a laborious, error prone and time-consuming process for manually describing rules mapping instances between two datasets. Thus, an automatic approach for solving this problem is more than welcome. In this paper, we propose a novel interlinking method, SERIMI, for solving this problem automatically. SERIMI matches instances between a source and a target datasets, without prior knowledge of the data, domain or schema of these datasets. Experiments conducted with benchmark collections demonstrate that our approach considerably outperforms state-of-the-art automatic approaches for solving the interlinking problem on the Linked Data Cloud. + |
| SLINT: A Schema-Independent Linked Data Interlinking System + | Linked data interlinking is the discovery of all instances that represent the same real-world object and locate in different data sources. Since different data publishers frequently use different schemas for storing resources, we aim at developing a schema-independent interlinking system. Our system automatically selects important predicates and useful predicate alignments, which are used as the key for blocking and instance matching. The key distinction of our system is the use of weighted co-occurrence and adaptive filtering in blocking and instance matching. Experimental results show that the system highly improves the precision and recall over some recent ones. The performance of the system and the efficiency of main steps are also discussed. + |
| SPLENDID: SPARQL Endpoint Federation Exploiting VOID Descriptions + | In order to leverage the full potential of the Semantic Web it is necessary to transparently query distributed RDF data sources in the same way as it has been possible with federated databases for ages. However, there are significant differences between the Web of (linked) Data and the traditional database approaches. Hence, it is not straightforward to adapt successful database techniques for RDF federation. Reasons are the missing cooperation between SPARQL endpoints and the need for detailed data statistics for estimating the costs of query execution plans. We have implemented SPLENDID, a query optimization strategy for federating SPARQL endpoints based on statistical data obtained from voiD descriptions. + |
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| Towards a Knowledge Graph Representing Research Findings by Semantifying Survey Articles + | Despite significant advances in technology, the way how research is done and especially communicated has not changed much. We have the vision that ultimately researchers will work on a common knowledge base comprising comprehensive descriptions of their research, thus making research contributions transparent and comparable. The current approach for structuring, systematizing and comparing research results is via survey or review articles. In this article, we describe how surveys for research fields can be represented in a semantic way, resulting in a knowledge graph that describes the individual research problems, approaches, implementations and evaluations in a structured and comparable way. We present a comprehensive ontology for capturing the content of survey articles. We discuss possible applications and present an evaluation of our approach with the retrospective, exemplary semantification of a survey. We demonstrate the utility of the resulting knowledge graph by using it to answer queries about the different research contributions covered by the survey and evaluate how well the query answers serve readers’ information needs, in comparison to having them extract the same information from reading a survey paper. + |
| Towards a Knowledge Graph for Science + | The document-centric workflows in science have reached (or already exceeded) the limits of adequacy. This is emphasized by recent discussions on the increasing proliferation of scientific literature and the reproducibility crisis. This presents an opportunity to rethink the dominant paradigm of document-centric scholarly information communication and transform it into knowledge-based information flows by representing and expressing information through semantically rich, interlinked knowledge graphs. At the core of knowledge-based information flows is the creation and evolution of information models that establish a common understanding of information communicated between stakeholders as well as the integration of these technologies into the infrastructure and processes of search and information exchange in the research library of the future. By integrating these models into existing and new research infrastructure services, the information structures that are currently still implicit and deeply hidden in documents can be made explicit and directly usable. This has the potential to revolutionize scientific work as information and research results can be seamlessly interlinked with each other and better matched to complex information needs. Furthermore, research results become directly comparable and easier to reuse. As our main contribution, we propose the vision of a knowledge graph for science, present a possible infrastructure for such a knowledge graph as well as our early attempts towards an implementation of the infrastructure. + |
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| Unveiling the hidden bride: deep annotation for mapping and migrating legacy data to the Semantic Web + | The success of the Semantic Web crucially depends on the easy creation, integration, and use of semantic data. For this purpose, we consider an integration scenario that defies core assumptions of current metadata construction methods. We describe a framework of metadata creation where Web pages are generated from a database and the database owner is cooperatively participating in the Semantic Web. This leads us to the deep annotation of the database—directly by annotation of the logical database schema or indirectly by annotation of the Web presentation generated from the database contents. From this annotation, one may execute data mapping and/or migration steps, and thus prepare the data for use in the Semantic Web. We consider deep annotation as particularly valid because: (i) dynamic Web pages generated from databases outnumber static Web pages, (ii) deep annotation may be a very intuitive way to create semantic data from a database, and (iii) data from databases should remain where it can be handled most efficiently—in its databases. Interested users can then query this data directly or choose to materialize the data as RDF files. + |
| Updating Relational Data via SPARQL/Update + | Relational Databases are used in most current enterprise environments to store and manage data. The semantics of the data is not explicitly encoded in the relational model, but implicitly on the application level. Ontologies and Semantic Web technologies provide explicit semantics that allows data to be shared and reused across application, enterprise, and community boundaries. Converting all relational data to RDF is often not feasible, therefore we adopt an ontology-based access to relational databases. While existing approaches focus on read-only access, we present our approach OntoAccess that adds ontology-based write access to relational data. OntoAccess consists of the update-aware RDB to RDF mapping language R3M and algorithms for translating SPARQL/Update operations to SQL. This paper presents the mapping language, the translation algorithms, and a prototype implementation of OntoAccess. + |
| Use of OWL and SWRL for Semantic Relational Database Translation + | General purpose query interfaces to relational databases can expose vast amounts of content to the Semantic Web. In this paper, we discuss Automapper, a tool that automatically generates data source and mapping ontologies using OWL and SWRL. We also describe the use of these ontologies in our Semantic Distributed Query architecture, an implementation for mapping RDF queries to disparate data sources, including SQL-compliant databases, using SPARQL as the query language. This paper covers Automapper functionality that exploits some of the expressiveness of OWL to produce more accurate translations. A comparison with related work on Semantic Web access to relational databases is also provided as well as an investigation into the use of OWL 1.1. + |
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| Zhishi.links Results for OAEI 2011 + | This report presents the results of Zhishi.links, a distributed instance matching system, for this year’s Ontology Alignment Evaluation Initiative (OAEI) campaign. We participate in Data Interlinking track (DI) of IM@OAEI2011. In this report, we briefly describe the architecture and matching strategies of Zhishi.links, followed by an analysis of the results. + |
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| Has type "Has type" is a predefined property that describes the datatype of a property and is provided by Semantic MediaWiki. | Text + |
