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'''VoID''' (from "Vocabulary of Interlinked Datasets") is an [[Resource Description Framework|RDF]] based schema to describe [[Linked data|linked datasets]]. With VoID the discovery and usage of linked datasets can be performed both effectively and efficiently. A dataset is a collection of data, published and maintained by a single provider, available as RDF, and accessible, for example, through [http://en.wikipedia.org/wiki/Dereferenceable_Uniform_Resource_Identifier dereferenceable HTTP URIs] or a [[SPARQL endpoint|SPARQL endpoint]]. == Overview == Basically, we find two classes at the heart of VoID: * A dataset (<code>void:Dataset</code>) is a collection of data, which is: ** published and maintained by a single provider, and ** available as RDF, and ** accessible, for example, through dereferenceable HTTP URIs or a SPARQL endpoint. * The interlinking is modelled by a linkset (<code>void:Linkset</code>). A linkset in voiD is a subclass of a dataset, used for storing triples to express the interlinking relationship between datasets. In each interlinking triple, the subject is a resource hosted in one dataset and the object is a resource hosted in another dataset. This modelling enables a flexible and powerful way to talk in great detail about the interlinking between two datasets, such as how many links there exist, which kind of links (e.g. <code>owl:sameAs</code> or <code>foaf:knows</code>) are present, or stating who claims these statements. In the following, the modelling of the interlinking in voiD is depicted: [[File:Void-linkset-conceptual.png|600px|center|frame|voiD interlinking concept]] The core resources of the VoID spec are as follows: # [http://rdfs.org/ns/void VoID vocabulary] (normative), defines the classes and properties (available in HTML and RDF) # [http://www.w3.org/TR/void/ Describing Linked Datasets with the VoID Vocabulary], explains the usage of VoID for both data publisher and consumer (along with other vocabularies such as [[Dublin Core]], [[FOAF]], etc.) # [http://code.google.com/p/void-impl/ VoID code repository], hosting exemplary implementations (also issues re the vocabulary are accessible there) == Using VoID == A simple VoID example that describes two well-known LOD datasets and their interlinking is shown in the following. @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix dcterms: <http://purl.org/dc/terms/> . @prefix void: <http://rdfs.org/ns/void#> . :DBpedia rdf:type void:Dataset ; foaf:homepage <http://dbpedia.org/> . :DBLP rdf:type void:Dataset ; foaf:homepage <http://www4.wiwiss.fu-berlin.de/dblp/all> ; dcterms:subject <http://dbpedia.org/resource/Computer_science> ; dcterms:subject <http://dbpedia.org/resource/Journal> ; dcterms:subject <http://dbpedia.org/resource/Proceedings> . :DBpedia void:subset :DBpedia2DBLP . :DBpedia2DBLP rdf:type void:Linkset ; void:target :DBpedia ; void:target :DBLP . Let us assume that the above VoID description has, for example, been gathered by a semantic indexer from the VoID documents data publishers provide along with their dataset. It is then possible to execute the following example query: SELECT DISTINCT ?dataset WHERE { ?dataset a void:Dataset . ?dataset dcterms:subject <http://dbpedia.org/resource/Journal> . } This query asks for all datasets that have been categorised as containing data about journals and will eventually return <tt>:DBLP</tt>. A slightly modified version of the query above applied to the [[VoID#RKB_explorer|RKB explorer]] is shown below: SELECT DISTINCT ?dataset WHERE { ?dataset a void:Dataset . ?dataset dcterms:subject <http://dbpedia.org/resource/Category:Computer_scientists> . } The above SPARQL query will list all datasets about computer scientists. Much more is possible with VoID, though. You can describe basic dataset metadata (such as publisher, license, etc.), vocabularies used, example resources, SPARQL endpoint availability, and of course the fine-grained interlinking between the datasets. Such an example, describing partly the interlinking between DBpedia and Geonames, is: :DBpedia void:subset :DBpedia2Geonames . :DBpedia2Geonames a void:Linkset ; void:linkPredicate owl:sameAs ; void:target :DBpedia ; void:target :Geonames . == Generating and Consuming == There are already tools and applications available that consume or produce VoID. === Generators & Editors === * [http://www.hpi.uni-potsdam.de/naumann/projects/btc voidGen] (Christoph Böhm, HPI, Universität Potsdam) ** Hadoop-based, scalable VoID generation ** This was used for [https://www.hpi.uni-potsdam.de/naumann/sites/btc2010/ Creating voiD Descriptions for Web-scale Data] (winner of the ISWC2010 Billion Triples Challenge Track) * VoID tools is a collection of Jena-based tools to support the generation of VoID descriptions including RDFStats statistics. * OpenLink's Virtuoso produced VoID, see [http://docs.openlinksw.com/virtuoso/fn_rdf_void_store.html DB.DBA.RDF_VOID_STORE] * liftSSM is an [http://code.google.com/p/void-impl/source/browse/#svn/trunk/liftSSM XSLT] that takes a [http://sw.deri.org/2007/07/sitemapextension/ semantic sitemap] in XML and creates a stub voiD description in RDF/XML. * The current [http://sw.deri.org/2006/08/nxparser/release/nxparser-1.1.jar version v1.1] of the [http://sw.deri.org/2006/08/nxparser/ NxParser] (Parser for NTriples, NQuads, and more) supports exporting VoID descriptions of statistics. * [http://lab.linkeddata.deri.ie/ve2/ ve2] - the2 '''V'''oID '''e'''ditor allows to manually generate a VoID file in RDF Turtle format, incl. the definition of the characteristics of your linked dataset, such as categories, interlinking, technical features, licensing, etc. Developed at [http://deri.ie/ DERI]. ** [http://openphacts.cs.man.ac.uk/Void-Editor/ Open PHACTS VoID editor] — Open PHACTS refers to a European initiative to create an "Open Pharmacological Space" where data is stored in RDF and datasets are described via VoID. The VoID editor developed for Open PHACTS is a direct descendent of the ve2 edtor developed at DERI * [https://metacpan.org/module/RDF::Generator::Void RDF::Generator::Void] - A Perl module to generate VoID descriptions. Can also be found in Debian as [http://packages.debian.org/sid/librdf-generator-void-perl librdf-generator-void-perl]. The current release compiles some statistics and uses some heuristics to extract vocabularies. Further data can be provided manually and it can also read an RDF model from a different source. The module [https://metacpan.org/module/RDF::LinkedData RDF::LinkedData] can be configured to use this module. The current release is an early beta. === Exploration, Browser, Stores === * At the [http://void.rkbexplorer.com/ VoID store] one can find, browse and query various VoID descriptions. * The [http://kwijibo.talis.com/voiD/ VoID Browser] allows to view and query VoID descriptions. * [http://lab.linkeddata.deri.ie/vox/ voX, the Dataset Explorer] allows to explore datasets. == Examples in the Wild == In the examples below, VoID is used for different purposes and use cases, however, the time it took people to implement it may be an indicator for how remarkably easy it is to generate/consume VoID. === Decimalised Database of Concepts === In the [http://purl.org/NET/decimalised decimalised database of concepts] (DDC) dataset, VoID is used extensively. DDC is a collection of topics suitable for use in linked data. It is inspired by the Dewey Decimal Classification, but no guarantees are made about the closeness of its resemblance as a whole. SKOS mapping links are provided from this database to the Dewey system, to Library of Congree Classification codes and to DBPedia resources where possible. === EPrints === [http://eprints.org EPrints] Repository software publishes RDF as of v3.2.1, and automatically describes the dataset using VoID. Suggestions for improvement to cjg@ecs.soton.ac.uk (it's worth getting right as many repositories will end up with this code) === Italian National Research Council (CNR) === Italian National Research Council (CNR) publishes organizational data at http://data.cnr.it/ and provides also a [http://data.cnr.it/data/http://data.cnr.it/dataset/ VoID description]. === Lingvoj === As [http://lists.w3.org/Archives/Public/public-lod/2009Aug/0093.html reported by Bernard Vatant], lingvoj has a [http://www.lingvoj.org/void VoID description] as well; lingvoj is a linked dataset dedicated to the publication and use of multilingual RDF descriptions of human languages. === LODStats === [http://stats.lod2.eu/ LODStats] attempts to compute comprehensive summaries and statistics for all LOD datasets on the Web. It uses VoID and the Data Cube Vocabulary to represent the statistics. [http://stats.lod2.eu/stat_result/4040.void Example for Europeana Linked Data] === Open Data Communities === [http://opendatacommunities.org/ Open Data Communities] uses VoID, see for example [http://opendatacommunities.org/datasets/imd-rank-2010.rdf Index of Multiple Deprivation Ranking, 2010]. === OECD Glossary of Statistics === [http://oecd.dataincubator.org/ oecd.dataincubator.org] is a dataset offering VoID about data extracted from the [http://stats.oecd.org/glossary/ OECD Glossary of Statistics]. === OpenLink Virtuoso === Since Virtuoso [http://sourceforge.net/project/shownotes.php?release_id=660861 5.0.10] (2009-02-13), OpenLink has included support for VoID. Further, Kingsley Idehen (CEO and founder of OpenLink) has [http://lists.w3.org/Archives/Public/public-lod/2009Jan/0099.html announced] a [http://linkeddata.uriburner.com/about/html/http://twitter.com/kidehen demo from their Virtuoso platform]: the [http://uriburner.com/ URIBurner] service turns structured HTML into RDF, and uses VoID to represent the (on the fly) generated data description. As [http://lists.w3.org/Archives/Public/public-lod/2009Mar/0044.html announced on 2009-03-05], OpenLink has generated a VoID graph for DBpedia; use <http://dbpedia.org/void/> for the default graph field at [http://dbpedia.org/sparql http://dbpedia.org/sparql]. Virtuoso (both Open- and Closed-Source variants) also now includes scripts which use built-in functions for VoID generation and storage, e.g., <code>[http://docs.openlinksw.com/virtuoso/fn_rdf_void_store.html DB.DBA.RDF_VOID_STORE]</code> === Ordnance Survey === Ordnance Survey, Great Britain's national mapping agency uses VoID to describe their [http://data.ordnancesurvey.co.uk/ data]. === PSI Catalogues Aggregator === The [http://bagatelles.ecs.soton.ac.uk/psi/federator/ PSI Catalogues Aggregator] offers voiD descriptions for Public Sector Information (PSI) catalogues. For example, see their [http://bagatelles.ecs.soton.ac.uk/psi/federator/data.gov.uk data.gov.uk] VoID description. === RAMON, Eurostat's Metadata Server === The Eurostat [http://ec.europa.eu/eurostat/ramon/ Metadata Server RAMON] uses [http://ec.europa.eu/eurostat/ramon/rdfdata/void.rdf VoID] to describe their data, including countries and NUTS codes. === RDFohloh === Sergio [http://lists.w3.org/Archives/Public/public-lod/2009Jan/0105.html announced] that [http://www.w3.org/2007/08/pyRdfa/extract?uri=http%3A//rdfohloh.wikier.org/about RDFohloh] has VoID descriptions. === RKB explorer === As [http://lists.w3.org/Archives/Public/public-lod/2009Jan/0055.html reported by Hugh Glaser], the [http://www.rkbexplorer.com/ RKB explorer] activity has a [http://void.rkbexplorer.com/ VoID site] which enables [http://void.rkbexplorer.com/sparql/ query] and [http://void.rkbexplorer.com/browse/ browse] for CRS datasets. For example: PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX void: <http://rdfs.org/ns/void#> PREFIX scovo: <http://purl.org/NET/scovo#> SELECT ?subjects ?objects ?stats WHERE { ?crs void:subjectsTarget ?subjects . ?crs void:objectsTarget ?objects . ?crs void:statItem ?item . ?item rdf:value ?stats } The interlinkage of the RKB sites can be [http://www.rkbexplorer.com/linkage/crs-linkage-neat.png visualised] from the VoID data. The VoID data for a particular RKB site can be accessed as Linked Data at that site, for example the [http://dblp.rkbexplorer.com/ dblp.rkbexplorer.com] site has a [http://dblp.rkbexplorer.com/models/void.ttl void.ttl file], [http://dblp.rkbexplorer.com/id/void voiD dataset URI] and [http://dblp.rkbexplorer.com/id/crs information about] its [http://dblp.rkbexplorer.com/crs/ CRS]. === RPI's Linked Data from data.gov === http://data-gov.tw.rpi.edu uses VoID to describe their datasets, see for example in an [http://data-gov.tw.rpi.edu/wiki/URI_design_for_RDF_conversion_of_CSV-based_data URI design] note. === SchemaCache === Talis' [http://schemacache.test.talis.com SchemaCache] publishes a [http://schemacache.test.talis.com/meta VoID description]. === SPARQL Endpoints Status === Mondeca provides a list of the availability of public SPARQL endpoints fetched dynamically using CKAN, using [http://labs.mondeca.com/vocab/endpointStatus/index.html VoID along with an extension] to describe the status of an endpoint. === The Stationery Office (TSO) === The UK-based 'The Stationery Office' (TSO) provides information management & publishing solutions to the public and private sectors and uses VoID to describe different [http://openuplabs.tso.co.uk/datasets UK datasets], see for example http://gov.tso.co.uk/gazettes/void === Telegraphis === Linked Data about currencies on telegraphis.net, see http://telegraphis.net/data/void === World Bank === [http://worldbank.270a.info/ World Bank Linked Data] has a [http://worldbank.270a.info/.well-known/void VoID] + SPARQL Service Description. == Feedback and Discussions == We have a [https://groups.google.com/group/void-discussion VoID discussion group] (void-discussion@googlegroups.com) if you are interested to share your experience or have a question. If you have a feature request or want to file a bug report, please use the [http://code.google.com/p/void-impl/issues/list VoID Issue Tracker]. Some of us hang out on #swig IRC channel at Freenode. == Related Specifications == There are some specifications that use or extend VoID or are related to it: * DCAT (Data Catalog vocabulary) - see http://vocab.deri.ie/dcat-overview * RDF HDT (Header-Dictionary-Triples) - see http://www.w3.org/Submission/HDT-Related/ * The Provenance Vocabulary - see http://purl.org/net/provenance/ * voidp: A Vocabulary for Data and Dataset Provenance - see http://www.enakting.org/provenance/voidp/ == See also == The VoID vocabulary is maintained by the voiD team: * [[Keith Alexander]] * [[Richard Cyganiak]] * [[Michael Hausenblas]] * [[Jun Zhao]] === by the VoID team === * [http://blogs.talis.com/n2/archives/914 voiD stores and Interesting Queries], Keith Alexander, blog post * [http://blogs.talis.com/n2/archives/485 voiD, datasets, graphs, documents, and dcterms:isPartOf backlinks], Keith Alexander, blog post * [http://www.slideshare.net/mediasemanticweb/void-talk-at-ldow09 voiD talk], Michael Hausenblas, LDOW09 * [http://webofdata.wordpress.com/2009/03/01/effective-and-efficient-discovery/ On the Effectiveness and Efficiency of Discovery], Michael Hausenblas, blog post * [http://blogs.talis.com/n2/archives/209 voiD: a Vocabulary of Interlinked Datasets], Keith Alexander, blog post * [http://www.talis.com/nodalities/pdf/nodalities_issue4.pdf Discovery and Usage of Linked Datasets on the Web of Data], Michael Hausenblas, NodMag #4 * [http://blogs.talis.com/n2/archives/tag/eswc2008 European Semantic Web Conference 2008 at Tenerife], Keith Alexander, blog post * [http://dowhatimean.net/2008/06/back-from-eswc-2008 Back from ESWC 2008], Richard Cyganiak, blog post * [http://www.slideshare.net/mediasemanticweb/full-eswc08-lightning-talk voiD - full ESWC08 lightning talk], Michael Hausenblas, slides === what others say about VoID === Aggregated references: * [http://scholar.google.com/scholar?hl=en&sciodt=0%2C5&q=&cites=1700814373301477402&as_sdt=2005&as_ylo=&as_vis=1 50+ citations] via Google Scholar (in early 2012) Listings: * [http://www.slideshare.net/pmika/making-things-findable Making things findable] Peter Mika, [http://wims.vestforsk.no/ WIMS2011] key note * [http://techstreams.wordpress.com/2010/04/04/practical-semantic-web-creating-a-catalog-of-linked-data/ Practical semantic web - creating a catalog of Linked data] Anand Mallaya, blog post * [http://www.iscb.org/cms_addon/conferences/cshals2010/presentations/SchultzCSHALS10.pdf Creating a Linked Data Architecture for Neuroscience] Tim Schultz, Johnson & Johnson * [http://www.cabinetoffice.gov.uk/media/301253/puiblic_sector_uri.pdf Designing URI Sets for the UK Public Sector] UK Chief Technology Officer Council * [http://c4i.gmu.edu/ursw/2009/papers/URSW2009_P1_Reynolds.pdf Uncertainty reasoning for linked data] (position paper at [http://c4i.gmu.edu/ursw/2009/ URSW09 workshop]) Dave Reynolds, HP labs * [http://www.biomedcentral.com/1471-2105/10/S10/S10 A journey to Semantic Web query federation in the life sciences] Kei-Hoi Cheung et al * [http://blogs.talis.com/nodalities/2009/07/linked-data-public-domain.php Linked Data and the Public Domain] Ian Davis, Talis, Nodalities blog * [http://andreasinica.blogspot.com/2009/07/articlereview-geographical-linked-data.html ArticleReview: Geographical Linked Data: The Administrative Geography of Great Britain on the Semantic Web], Andrea Huang, blog post * [http://blogs.talis.com/nodalities/2009/04/discovering-sparql.php Discovering SPARQL], Alex Tucker, Talis blog post * [http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JanMar/0186.html service descriptions: comparison of VoiD, DARQ, and SADDLE], Gregory Williams, post to public-rdf-dawg@w3.org * [http://lists.w3.org/Archives/Public/public-lod/2009Mar/0044.html VoiD graph for DBpedia], Kingsley Idehen, post to public-lod@w3.org * [http://lists.w3.org/Archives/Public/public-lod/2009Mar/0024.html On the relation of voiD and Silk], Chris Bizer, post to public-lod@w3.org * [http://bnode.org/blog/2009/02/18/linked-data-value-spiral The Linked Data Value Spiral], Benjamin Nowack, blog post * [http://www.openlinksw.com/weblog/oerling/lodw.pdf Faceted Views over Large-Scale Linked Data], Orri Erling, short paper submission to LDOW09, a WWW09 workshop * [http://clarkparsia.com/weblog/2009/02/04/distributed-query-pellet-into-the-void/ Distributed Query: Pellet into the voiD], Kendall Clark, blog post * [http://blogs.talis.com/nodalities/2009/01/void-linking-linked-data.php voiD: Linking Linked Data], Zach Beauvais, Talis blog post * [http://efoundations.typepad.com/efoundations/2009/01/surveying-with-void.html Surveying with voiD], PeteJ, eFoundations, blog post * [http://www.openlinksw.com/weblog/oerling/?id=1510 Linked Data & The Year 2009 (updated)], Orri Erling, blog post * [http://ftp.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-401/iswc2008pd_submission_69.pdf Optimizing SPARQL Queries over Disparate RDF Data Sources through Distributed Semi-Joins], Jan Zemanek, Simon Schenk, ISWC2008 Posters and Demonstrations * [http://www.openlinksw.com/weblog/oerling/?id=1377 VOID, Or Will the LOD Cloud bring Rain?], Orri Erling, blog post * [http://blog.aldobucchi.com/2008/08/linked-data-metadata-introspecting.html Linked Data Metadata. Introspecting the Semantic Web], Aldo Bucchi, blog post * [http://blog.dbtune.org/post/2008/06/12/Describing-the-content-of-RDF-datasets Describing the content of RDF datasets], Yves Raimond, blog post * [http://esw.w3.org/topic/FindingResourceDescriptions Uniform Access to Links and Properties] via W3C ESW Wiki [[Category:Vocabulary]] [[Category:Ontology]] [[Category:Documentation]]
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