Semantic Web - Volume 7, issue 2

Authors: Hogan, Aidan | Hitzler, Pascal | Janowicz, Krzysztof

Article Type: Editorial

Abstract: Since 2012, the Semantic Web journal has been accepting papers in a novel Linked Dataset description track. Here we motivate the track and provide some analysis of the papers accepted thus far. We look at the ratio of accepted papers in this time-frame that fall under this track, the relative impact of these papers in terms of citations, and we perform a technical analysis of the datasets they describe to see what sorts of resources they provide and to see if the datasets have remained available since publication. Based on a variety of such analyses, we present some lessons …learnt and discuss some potential changes we could apply to the track in order to improve the overall quality of papers accepted. Show more

Keywords: Linked Data, SPARQL, Linked Dataset, scientometrics

DOI: 10.3233/SW-160216

Citation: Semantic Web, vol. 7, no. 2, pp. 105-116, 2016

Authors: Stefanova, Silvia | Risch, Tore

Article Type: Research Article

Abstract: We present an approach for scalable long-term preservation of data stored in relational databases (RDBs) as RDF, implemented in the SAQ (Semantic Archive and Query) system. The proposed approach is suitable for archiving scientific data used in scientific publications where it is desirable to preserve only parts of an RDB, e.g. only data about a specific set of experimental artefacts in the database. With the approach, long-term preservation as RDF of selected parts of a database is specified as an archival query in an extended SPARQL dialect, A-SPARQL . The query processing is based on automatically generating an RDF …view of a relational database to archive, called the RD-view . A-SPARQL provides flexible selection of data to be archived in terms of a SPARQL-like query to the RD-view. The result of an archival query is a data archive file containing the RDF-triples representing the relational data content to be preserved. The system also generates a schema archive file where sufficient meta-data are saved to allow the archived database to be fully reconstructed. An archival query usually selects both properties and their values for sets of subjects, which makes the property p in some triple patterns unknown. We call such queries where properties are unknown unbound-property queries . To achieve scalable data preservation and recreation, we propose some query transformation strategies suitable for optimizing unbound-property queries. These query rewriting strategies were implemented and evaluated in a new benchmark for archival queries called ABench . ABench is defined as set of typical A-SPARQL queries archiving selected parts of databases generated by the Berlin benchmark data generator. In experiments, the SAQ optimization strategies were evaluated by measuring the performance of A-SPARQL queries selecting triples for archival in ABench. The performance of equivalent SPARQL queries for related systems was also measured. The results showed that the proposed optimizations substantially improve the query execution time for archival queries. Show more

Keywords: Database archival, benchmark, SPARQL optimization, SPARQL views of relational databases, unbound-property queries

DOI: 10.3233/SW-150173

Citation: Semantic Web, vol. 7, no. 2, pp. 117-137, 2016

Authors: Stutz, Philip | Strebel, Daniel | Bernstein, Abraham

Article Type: Research Article

Abstract: Both researchers and industry are confronted with the need to process increasingly large amounts of data, much of which has a natural graph representation. Some use MapReduce for scalable processing, but this abstraction is not designed for graphs and has shortcomings when it comes to both iterative and asynchronous processing, which are particularly important for graph algorithms. This paper presents the Signal/Collect programming model for scalable synchronous and asynchronous graph processing. We show that this abstraction can capture the essence of many algorithms on graphs in a concise and elegant way by giving Signal/Collect adaptations of algorithms that solve …tasks as varied as clustering, inferencing, ranking, classification, constraint optimisation, and even query processing. Furthermore, we built and evaluated a parallel and distributed framework that executes algorithms in our programming model. We empirically show that our framework efficiently and scalably parallelises and distributes algorithms that are expressed in the programming model. We also show that asynchronicity can speed up execution times. Our framework can compute a PageRank on a large (>1.4 billion vertices, >6.6 billion edges) real-world graph in 112 seconds on eight machines, which is competitive with other graph processing approaches. Show more

Keywords: Distributed computing, scalability, programming abstractions, programming models, graph processing

DOI: 10.3233/SW-150176

Citation: Semantic Web, vol. 7, no. 2, pp. 139-166, 2016

Authors: Constantin, Alexandru | Peroni, Silvio | Pettifer, Steve | Shotton, David | Vitali, Fabio

Article Type: Research Article

Abstract: The availability in machine-readable form of descriptions of the structure of documents, as well as of the document discourse (e.g. the scientific discourse within scholarly articles), is crucial for facilitating semantic publishing and the overall comprehension of documents by both users and machines. In this paper we introduce DoCO , the Document Components Ontology , an OWL 2 DL ontology that provides a general-purpose structured vocabulary of document elements to describe both structural and rhetorical document components in RDF. In addition to giving a formal description of the ontology, this paper showcases its utility in practice in a variety of …our own applications and other activities of the Semantic Publishing community that rely on DoCO to annotate and retrieve document components of scholarly articles. Show more

Keywords: DEO, DoCO, PDFX, SPAR ontologies, Utopia Documents, document components, rhetoric, structural patterns

DOI: 10.3233/SW-150177

Citation: Semantic Web, vol. 7, no. 2, pp. 167-181, 2016

Authors: Daga, Enrico | d’Aquin, Mathieu | Adamou, Alessandro | Brown, Stuart

Article Type: Research Article

Abstract: The article reports on the evolution of data.open.ac.uk , the Linked Open Data platform of the Open University, from a research experiment to a data hub for the open content of the University. Entirely based on Semantic Web technologies (RDF and the Linked Data principles), data.open.ac.uk  is used to curate, publish and access data about academic degree qualifications, courses, scholarly publications and open educational resources of the University. It exposes a SPARQL endpoint and several other services to support developers, including queries stored server-side and entity lookup using known identifiers such as course codes and YouTube video IDs. The platform …is now a key information service at the Open University, with several core systems and websites exploiting linked data through data.open.ac.uk . Through these applications, data.open.ac.uk  is now fulfilling a key role in the overall data infrastructure of the university, and in establishing connections with other educational institutions and information providers. Show more

Keywords: Linked Open Data, dataset, university data, education

DOI: 10.3233/SW-150182

Citation: Semantic Web, vol. 7, no. 2, pp. 183-191, 2016

Authors: Khrouf, Houda | Troncy, Raphaël

Article Type: Research Article

Abstract: An ever increasing amount of event-centric knowledge is spread over multiple web sites, either materialized as calendar of past and upcoming events or illustrated by cross-media items. This opens an opportunity to create an infrastructure unifying event-centric information derived from event directories, media platforms and social networks. In order to create such infrastructure, EventMedia relies on Semantic Web technologies that ensures seamless aggregation and integration of disparate data sources, some of which overlap in their coverage. In this paper, we present the EventMedia dataset composed of events descriptions associated with media and interlinked with the Linked Open Data cloud. We …describe how data has been extracted, converted, interlinked and published following the best practices of the Semantic Web. Show more

Keywords: Events, Linked Data, social media, LODE ontology

DOI: 10.3233/SW-150184

Citation: Semantic Web, vol. 7, no. 2, pp. 193-199, 2016

Authors: Cox, Simon J.D.

Article Type: Research Article

Abstract: We have extended OWL-Time to support the encoding of temporal position in a range of reference systems, in addition to the Gregorian calendar and conventional clock. Two alternative implementations are provided: as a pure extension or OWL-Time, or as a replacement, both of which preserve the same representation for the cases originally supported by OWL-Time. The combination of the generalized temporal position encoding and the temporal interval topology from OWL-Time support a range of applications in a variety of cultural and technical settings. These are illustrated with examples involving non-Gregorian calendars, Unix-time, and geologic time using both chronometric and stratigraphic …timescales. Show more

Keywords: Temporal reference system, calendar, temporal topology, ontology re-use

DOI: 10.3233/SW-150187

Citation: Semantic Web, vol. 7, no. 2, pp. 201-209, 2016