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<body onload="adjustWidthOfImages()" class="h-entry informative"><div class="head">
<a href="https://www.w3.org/" class="logo"><img alt="W3C" width="72" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C"></a> <h1 id="title" class="title p-name">DDI-RDF Discovery Vocabulary</h1>
<h2 id="subtitle" class="subtitle">A vocabulary for publishing metadata about data sets (research and survey data) into the Web of Linked Data</h2>
<h2>
<abbr title="World Wide Web Consortium">W3C</abbr> Document
<time class="dt-published" datetime="2019-03-21">21 March 2019</time>
</h2>
<dl>
<dt>Editors:</dt>
<dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.dr-thomashartmann.de/">Thomas Hartmann (formerly Bosch)</a></dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="https://www.linkedin.com/in/cygri">Richard Cyganiak</a>
(<a class="p-org org h-org h-card" href="http://www.topquadrant.com/">TopQuadrant</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="https://www.gesis.org/institut/mitarbeiterverzeichnis/person/?tx_gextstaffdir_staffdirectory%5bemail%[email protected]">Joachim Wackerow</a>
(<a class="p-org org h-org h-card" href="http://www.gesis.org/">GESIS - Leibniz Institute for the Social Sciences, Germany</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="https://www.gesis.org/institut/mitarbeiterverzeichnis/person/?tx_gextstaffdir_staffdirectory%5bemail%[email protected]">Benjamin Zapilko</a>
(<a class="p-org org h-org h-card" href="http://www.gesis.org/">GESIS - Leibniz Institute for the Social Sciences, Germany</a>)
</dd>
<dt>
Authors:
</dt><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.dr-thomashartmann.de/">Thomas Hartmann (formerly Bosch)</a></dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://csarven.ca/">Sarven Capadisli</a>
(<a class="p-org org h-org h-card" href="http://eis.iai.uni-bonn.de/">Enterprise Information Systems (EIS)</a>)
</dd><dd class="p-author h-card vcard"><span class="p-name fn">Franck Cotton</span>
(<a class="p-org org h-org h-card" href="http://www.insee.fr/en/default.asp">INSEE - Institut National de la Statistique et des Études Économiques, France</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="https://www.linkedin.com/in/cygri">Richard Cyganiak</a>
(<a class="p-org org h-org h-card" href="http://www.topquadrant.com/">TopQuadrant</a>)
</dd><dd class="p-author h-card vcard"><span class="p-name fn">Arofan Gregory</span>
(<a class="p-org org h-org h-card" href="http://www.opendatafoundation.org/">ODaF - Open Data Foundation, USA</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.aifb.kit.edu/web/Benedikt_K%C3%A4mpgen/en">Benedikt Kämpgen</a>
(<a class="p-org org h-org h-card" href="http://www.aifb.kit.edu/web/Hauptseite/en">Institute of Applied Informatics and Formal Description Methods (AIFB), Germany</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="https://www.gu.se/english/about_the_university/staff/?languageId=100001&userId=xoolof&departmentId=169030">Olof Olsson</a>
(<a class="p-org org h-org h-card" href="http://snd.gu.se/en">SND - Swedish National Data Service</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.heikopaulheim.com/">Heiko Paulheim</a>
(<a class="p-org org h-org h-card" href="http://dws.informatik.uni-mannheim.de/">Data and Web Science Group, University of Mannheim, Germany</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.gesis.org/en/institute/staff/?alpha=W&name=joachim%2Cwackerow">Joachim Wackerow</a>
(<a class="p-org org h-org h-card" href="http://www.gesis.org/">GESIS - Leibniz Institute for the Social Sciences, Germany</a>)
</dd><dd class="p-author h-card vcard"><a class="u-url url p-name fn" href="http://www.gesis.org/en/institute/staff/?alpha=Z&name=benjamin%2Czapilko">Benjamin Zapilko</a>
(<a class="p-org org h-org h-card" href="http://www.gesis.org/">GESIS - Leibniz Institute for the Social Sciences, Germany</a>)
</dd>
</dl>
<p>
This document is also available in this non-normative format:
<a rel="alternate" href="DDI-RDF_Discovery_Vocabulary.pdf">PDF</a>
</p>
<p class="copyright">
<a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
©
2019
<a href="https://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="https://www.keio.ac.jp/">Keio</a>,
<a href="https://ev.buaa.edu.cn/">Beihang</a>).
<abbr title="World Wide Web Consortium">W3C</abbr> <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
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apply.
</p>
<hr title="Separator for header">
</div>
<section id="abstract" class="introductory"><h2>Abstract</h2>
This specification defines the DDI-RDF Discovery Vocabulary (Disco), an RDF Schema vocabulary that enables discovery of research and survey data on the Web. It is based on <a href="http://www.ddialliance.org/what">DDI (Data Documentation Initiative)</a> XML formats.
</section>
<section id="sotd" class="introductory"><h2>Status of This Document</h2><p>
This document is merely a <abbr title="World Wide Web Consortium">W3C</abbr>-internal
document. It has no
official standing of any kind and does not represent consensus of
the <abbr title="World Wide Web Consortium">W3C</abbr> Membership.
</p>
<p>
The DDI-RDF Discovery Vocabulary is a draft specification of the DDI Alliance.
</p>
<p>This specification is produced by the subgroup on Disco (chair Joachim Wackerow) of the
<a href="http://www.ddialliance.org/alliance/working-groups#RDF">RDF Vocabularies Working Group</a>,
a working group at the <a href="http://www.ddialliance.org/alliance">DDI Alliance</a>.</p>
<p>Resources:</p>
<ul>
<li><a href="http://www.ddialliance.org/Specification/RDF/Discovery">Webpage at DDI Alliance</a></li>
<li><a href="https://groups.google.com/group/ddi-rdf-vocabulary">Google Group</a></li>
<li><a href="https://github.com/linked-statistics/disco-spec/issues">Issue tracker</a></li>
<li><a href="https://github.com/linked-statistics/disco-spec/">GitHub repository</a></li>
</ul>
</section><nav id="toc"><h2 class="introductory" id="table-of-contents">Table of Contents</h2><ol class="toc"><li class="tocline"><a class="tocxref" href="#tof"><span class="secno">1. </span>Table of Figures</a></li><li class="tocline"><a class="tocxref" href="#introduction"><span class="secno">2. </span>Introduction</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#scope-and-purpose"><span class="secno">2.1 </span>Scope and Purpose</a></li><li class="tocline"><a class="tocxref" href="#about-ddi"><span class="secno">2.2 </span>About DDI</a></li><li class="tocline"><a class="tocxref" href="#relationship-to-data-cube-dcat-and-xkos"><span class="secno">2.3 </span>Relationship to Data Cube, DCAT and XKOS</a></li></ol></li><li class="tocline"><a class="tocxref" href="#overview"><span class="secno">3. </span>Overview</a></li><li class="tocline"><a class="tocxref" href="#example"><span class="secno">4. </span>Real-life Example</a></li><li class="tocline"><a class="tocxref" href="#study"><span class="secno">5. </span>Studies and StudyGroups</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#coverage-references-to-ddi-xml-files-and-kind-of-data"><span class="secno">5.1 </span>Coverage, References to DDI-XML Files, and Kind of Data</a></li><li class="tocline"><a class="tocxref" href="#relationships-to-agents"><span class="secno">5.2 </span>Relationships to Agents</a></li><li class="tocline"><a class="tocxref" href="#analysis-units-and-universes"><span class="secno">5.3 </span>Analysis Units and Universes</a></li></ol></li><li class="tocline"><a class="tocxref" href="#metadata"><span class="secno">6. </span>General Metadata</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#identification"><span class="secno">6.1 </span>Identification</a></li><li class="tocline"><a class="tocxref" href="#versioning-information"><span class="secno">6.2 </span>Versioning Information</a></li><li class="tocline"><a class="tocxref" href="#links-to-related-files"><span class="secno">6.3 </span>Links to Related Files</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#access-rights-statements-and-licenses"><span class="secno">6.4 </span>Access Rights Statements and Licenses</a></li><li class="tocline"><a class="tocxref" href="#coverage-of-studies-logical-datasets-and-data-files"><span class="secno">6.5 </span>Coverage of Studies, Logical Datasets, and Data Files</a></li><li class="tocline"><a class="tocxref" href="#other-general-dublin-core-metadata-properties"><span class="secno">6.6 </span>Other General Dublin Core Metadata Properties</a></li></ol></li><li class="tocline"><a class="tocxref" href="#dataset"><span class="secno">7. </span>Data Sets, Data Files, and Descriptive Statistics</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#logicaldataset"><span class="secno">7.1 </span>LogicalDataSet</a></li><li class="tocline"><a class="tocxref" href="#datafile"><span class="secno">7.2 </span>DataFile</a></li><li class="tocline"><a class="tocxref" href="#descriptivestatistics"><span class="secno">7.3 </span>DescriptiveStatistics</a></li></ol></li><li class="tocline"><a class="tocxref" href="#variable"><span class="secno">8. </span>Variables, Variable Definitions, Representations, and Concepts</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#variable-and-variable-definition"><span class="secno">8.1 </span>Variable and Variable Definition</a></li><li class="tocline"><a class="tocxref" href="#representation"><span class="secno">8.2 </span>Representation</a></li><li class="tocline"><a class="tocxref" href="#codes-and-categories"><span class="secno">8.3 </span>Codes and Categories</a></li><li class="tocline"><a class="tocxref" href="#ordering"><span class="secno">8.4 </span>Ordering</a></li></ol></li><li class="tocline"><a class="tocxref" href="#collection"><span class="secno">9. </span>Data Collection</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#instrument"><span class="secno">9.1 </span>Instrument</a></li><li class="tocline"><a class="tocxref" href="#question"><span class="secno">9.2 </span>Question</a></li></ol></li><li class="tocline"><a class="tocxref" href="#useOfOtherVocabularies"><span class="secno">10. </span>Use of Other Vocabularies</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#dcmi-metadata-terms-dcmi"><span class="secno">10.1 </span>DCMI Metadata Terms (DCMI)</a></li><li class="tocline"><a class="tocxref" href="#simple-knowledge-organization-system-skos"><span class="secno">10.2 </span>Simple Knowledge Organization System (SKOS)</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#data-catalog-vocabulary-dcat"><span class="secno">10.3 </span>Data Catalog Vocabulary (DCAT)</a></li><li class="tocline"><a class="tocxref" href="#friend-of-a-friend-foaf-and-organization-ontology-org"><span class="secno">10.4 </span>Friend of a Friend (FOAF) and Organization Ontology (ORG)</a></li><li class="tocline"><a class="tocxref" href="#adms"><span class="secno">10.5 </span>Asset Description Metadata Schema (ADMS)</a></li><li class="tocline"><a class="tocxref" href="#prov-ontology-prov-o"><span class="secno">10.6 </span>PROV Ontology (PROV-O)</a></li><li class="tocline"><a class="tocxref" href="#rdf-data-cube-vocabulary-qb"><span class="secno">10.7 </span>RDF Data Cube Vocabulary (QB)</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#skos-extension-for-statistics-xkos"><span class="secno">10.8 </span>SKOS Extension for Statistics (XKOS)</a></li><li class="tocline"><a class="tocxref" href="#semanticscience-integrated-ontology-sio"><span class="secno">10.9 </span>Semanticscience Integrated Ontology (SIO)</a></li></ol></li><li class="tocline"><a class="tocxref" href="#mapping-from-DDI-XML-to-DDI-RDF"><span class="secno">11. </span>DDI-XML Bidirectional Mappings</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#representation-of-mappings-in-rdf"><span class="secno">11.1 </span>Representation of Mappings in RDF</a></li><li class="tocline"><a class="tocxref" href="#classes"><span class="secno">11.2 </span>Classes</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#object-properties"><span class="secno">11.3 </span>Object Properties</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#data-properties"><span class="secno">11.4 </span>Data Properties</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#overview-of-the-mapping-from-ddi-c-and-ddi-l-to-ddi-rdf"><span class="secno">11.5 </span>Overview of the Mapping from DDI-C and DDI-L to DDI-RDF</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#mapping-from-ddi-c-to-ddi-rdf"><span class="secno">11.6 </span>Mapping from DDI-C to DDI-RDF</a><ol class="toc"></ol></li><li class="tocline"><a class="tocxref" href="#mapping-from-ddi-l-to-ddi-rdf"><span class="secno">11.7 </span>Mapping from DDI-L to DDI-RDF</a><ol class="toc"></ol></li></ol></li><li class="tocline"><a class="tocxref" href="#implementations"><span class="secno">12. </span>Reference Implementations</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#microdata-information-system-missy"><span class="secno">12.1 </span>Microdata Information System (MISSY)</a><ol class="toc"></ol></li></ol></li><li class="tocline"><a class="tocxref" href="#limitations"><span class="secno">13. </span>Limitations</a></li><li class="tocline"><a class="tocxref" href="#vocabulary-reference"><span class="secno">A. </span>Vocabulary Reference</a></li><li class="tocline"><a class="tocxref" href="#combined-uml-diagram"><span class="secno">B. </span>Combined UML Diagram</a></li><li class="tocline"><a class="tocxref" href="#use-cases-and-example-queries"><span class="secno">C. </span>Use Cases and Example Queries</a></li><li class="tocline"><a class="tocxref" href="#acknowledgements"><span class="secno">D. </span>Acknowledgements</a></li><li class="tocline"><a class="tocxref" href="#references"><span class="secno">E. </span>References</a><ol class="toc"><li class="tocline"><a class="tocxref" href="#normative-references"><span class="secno">E.1 </span>Normative references</a></li><li class="tocline"><a class="tocxref" href="#informative-references"><span class="secno">E.2 </span>Informative references</a></li></ol></li></ol></nav>
<section id="tof">
<!-- placeholder for generated table of diagrams -->
<!--OddPage--><h2 id="x1-table-of-figures"><span class="secno">1. </span>Table of Figures<a class="self-link" aria-label="§" href="#tof"></a></h2><ul class="tof"><li class="tofline">
<a class="tocxref" href="#fig-vocabulary-overview">Figure <span class="figno">1</span> <span class="fig-title">Vocabulary Overview</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-overview">Figure <span class="figno">2</span> <span class="fig-title">Overview</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-coverage-and-universe">Figure <span class="figno">3</span> <span class="fig-title">Coverage and Universe</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-access-policy">Figure <span class="figno">4</span> <span class="fig-title">Access Policy</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-questionnaires">Figure <span class="figno">5</span> <span class="fig-title">Questionnaires</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-variables-list">Figure <span class="figno">6</span> <span class="fig-title">Variables List</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-variable-details">Figure <span class="figno">7</span> <span class="fig-title">Variable Details</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-concept-variable-link">Figure <span class="figno">8</span> <span class="fig-title">Concept-Variable Link</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-general-data-set-information">Figure <span class="figno">9</span> <span class="fig-title">General Data Set Information</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-coverage-references-to-ddi-xml-files-and-kind-of-data">Figure <span class="figno">10</span> <span class="fig-title">Coverage, References to DDI-XML Files, and Kind of Data</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-relationships-to-agents">Figure <span class="figno">11</span> <span class="fig-title">Relationships to Agents</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-study-universe-and-analysisunit">Figure <span class="figno">12</span> <span class="fig-title">Study, Universe and AnalysisUnit</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-identification">Figure <span class="figno">13</span> <span class="fig-title">Identification</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-versioning-information">Figure <span class="figno">14</span> <span class="fig-title">Versioning Information</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-links-to-related-files">Figure <span class="figno">15</span> <span class="fig-title">Links to Related Files</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-access-rights-statements-and-licenses">Figure <span class="figno">16</span> <span class="fig-title">Access Rights Statements and Licenses</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-study-coverage">Figure <span class="figno">17</span> <span class="fig-title">Study Coverage</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-logicaldataset-coverage">Figure <span class="figno">18</span> <span class="fig-title">LogicalDataSet Coverage</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-datafile-coverage">Figure <span class="figno">19</span> <span class="fig-title">DataFile Coverage</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-overview-data-sets-data-files-descriptive-statistics">Figure <span class="figno">20</span> <span class="fig-title">Overview: Data Sets, Data Files, Descriptive Statistics</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-logicaldataset">Figure <span class="figno">21</span> <span class="fig-title">LogicalDataSet</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-datafile">Figure <span class="figno">22</span> <span class="fig-title">DataFile</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-descriptivestatistics">Figure <span class="figno">23</span> <span class="fig-title">DescriptiveStatistics</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-example-category-statistics-frequency-table-of-variable-partliv-issp-2011">Figure <span class="figno">24</span> <span class="fig-title">Example Category Statistics: Frequency Table of Variable PARTLIV (ISSP 2011)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-example-category-statistics-frequency-table-of-variable-wrkhrs-issp-2011">Figure <span class="figno">25</span> <span class="fig-title">Example Category Statistics: Frequency Table of Variable WRKHRS (ISSP 2011)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-example-summary-statistics-descriptive-statistics-of-variable-wrkhrs-issp-2011">Figure <span class="figno">26</span> <span class="fig-title">Example Summary Statistics: Descriptive Statistics of Variable WRKHRS (ISSP 2011)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-summary-statistics">Figure <span class="figno">27</span> <span class="fig-title">Summary Statistics</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-category-statistics">Figure <span class="figno">28</span> <span class="fig-title">Category Statistics</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-variables-variable-definitions-representations-and-concepts">Figure <span class="figno">29</span> <span class="fig-title">Variables, Variable Definitions, Representations, and Concepts</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-variables-and-representedvariables">Figure <span class="figno">30</span> <span class="fig-title">Variables and RepresentedVariables</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-representation">Figure <span class="figno">31</span> <span class="fig-title">Representation</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-skos-concept-and-skos-conceptscheme">Figure <span class="figno">32</span> <span class="fig-title">skos:Concept and skos:ConceptScheme</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-example-category-statistics-frequency-table-of-variable-partliv-issp-2011-0">Figure <span class="figno">33</span> <span class="fig-title">Example Category Statistics: Frequency Table of Variable PARTLIV (ISSP 2011)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-example-category-statistics-frequency-table-of-variable-partliv-issp-2011-1">Figure <span class="figno">34</span> <span class="fig-title">Example Category Statistics: Frequency Table of Variable PARTLIV (ISSP 2011)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-datacollection">Figure <span class="figno">35</span> <span class="fig-title">DataCollection</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-representation-of-mappings-in-rdf">Figure <span class="figno">36</span> <span class="fig-title">Representation of Mappings in RDF</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-combined-uml-diagram-object-properties-only">Figure <span class="figno">37</span> <span class="fig-title">Combined UML Diagram (object properties only)</span></a>
</li><li class="tofline">
<a class="tocxref" href="#fig-statistical-classification-anzsic">Figure <span class="figno">38</span> <span class="fig-title">Statistical classification – ANZSIC</span></a>
</li></ul></section>
<section id="introduction">
<!--OddPage--><h2 id="x2-introduction"><span class="secno">2. </span>Introduction<a class="self-link" aria-label="§" href="#introduction"></a></h2>
<p>
The namespace for all terms in this ontology is: http://rdf-vocabulary.ddialliance.org/discovery#".
</p>
<p>
Normative formats of the DDI-RDF Discovery Vocabulary specification are
</p><ul>
<li>this HTML specification, and </li>
<li>the <a href="https://raw.github.com/linked-statistics/disco-spec/master/discovery.ttl">Turtle</a> file.</li>
</ul>
<p></p>
<p>
There is also a <a href="https://raw.github.com/linked-statistics/disco-spec/master/discovery.xml">non-canonical RDF/XML version</a> of the Turtle file.
</p>
<p>
Open issues are discussed on the issue tracker: <a href="https://github.com/linked-statistics/disco-spec/issues">open issues</a>.
</p>
<p>
A detailed overview of the Disco vocabulary is available as <a href="http://www.essepuntato.it/lode/owlapi/https://raw.github.com/linked-statistics/disco-spec/master/discovery.ttl">LODE view</a>
or a <a href="http://vowl.visualdataweb.org/webvowl/index.html#iri=http://rdf-vocabulary.ddialliance.org/discovery.ttl">web view</a> using the web application <a href="http://vowl.visualdataweb.org/webvowl.html">Web-based Visualization of Ontologies</a>.
</p>
<p>
For a detailed explanation of DDI terms please refer to <a href="#overview">section 2</a>.
</p>
<section id="scope-and-purpose">
<h3 id="x2-1-scope-and-purpose"><span class="secno">2.1 </span>Scope and Purpose<a class="self-link" aria-label="§" href="#scope-and-purpose"></a></h3>
<p>This specification is designed to support the discovery of
microdata sets and related metadata using RDF technologies in the
Web of Linked Data. Many archives and other organizations have
large amounts of data, sometimes publically available, but often
confidential in nature, requiring applications for access. Many
such organizations use the
<a href="http://www.ddialliance.org/what">Data Documentation Initiative</a>
standard, which is a proven and highly detailed XML metadata
format for describing rectangular data sets of this type.
This vocabulary makes use of the DDI specification to create a
simplified version of this model for the discovery of data files.</p>
<p>The data holdings of data archives are often collected by
researchers, and only afterwards disseminated by archives. Other
data-producing organizations such as research centers and
statistical agencies are also increasingly interested in the
DDI standards for documenting their own microdata. In general
terms, most DDI metadata describes data sets for the social,
behavioural, and economic sciences. This data is fairly
consistent in format, consisting of rectangular data files with
columns containing variables for a set of cases, contained in
the rows. It is often collected by survey, although in some
cases may come from administrative sources, sensors, or
registers.</p>
<p>This vocabulary is intended not only for use by the research
data community, but also by any others needing an RDF vocabulary
for describing this type of rectangular data. This vocabulary
will provide a useful model for describing some of the data sets
now being published by open government initiatives, by providing
a rich metadata structure for them. While the data sets may be
available (typically as CSV files) the metadata which
accompanies them is not necessarily coherent, making the
discovery of these data sets difficult. This vocabulary would
help to overcome this difficulty by allowing for the creation of
standard queries to programmatically identify data sets, whether
made available by government or held within a data archive.</p>
<p>
Disco could be used to discover datasets by searching for specific questions, topics, and geographical coverage.
Depending on the complexity of the search respectively of the data portal, parts of Disco could be used, the complete Disco, or Disco together with related vocabularies.
The document [<cite><a class="bibref" href="#bib-Scenarios">Scenarios</a></cite>] by Vompras, Gregory, Bosch, Capadisli, and Wackerow describes typical use cases for the applicability of the DDI-RDF Discovery vocabulary. In the Section <a class="bibref" href="#use-cases-and-example-queries">Use Cases and Example Queries</a> of the Appendix additional discovery use cases are illustrated by several SPARQL queries.</p>
</section>
<p>
Statistical domain experts (core members of the DDI Alliance Technical Implementation Committee,
representatives of national statistical institutes, national data archives) and Linked Open Data community
members have selected the DDI elements which are seen as most important to solve problems associated with
use cases in the area of data discovery. Section 2 gives an overview of the conceptual model.
More detailed descriptions of all the properties are given in the specification and two conference papers [<cite><a class="bibref" href="#bib-Linked-Statistical-Data">Linked-Statistical-Data</a></cite>] [<cite><a class="bibref" href="#bib-DDI-RDF-Discovery-Vocabulary">DDI-RDF-Discovery-Vocabulary</a></cite>].
Disco is intended to provide means to describe microdata by essential metadata for the discovery purpose.
Existing DDI-XML instances can be transformed into this RDF format and therefore exposed as Linked Data.
The vice-versa process is not intended, as we have defined Disco components and reused components of other
RDF vocabularies which make only sense in the Linked Data field.
</p>
<section id="about-ddi">
<h3 id="x2-2-about-ddi"><span class="secno">2.2 </span>About DDI<a class="self-link" aria-label="§" href="#about-ddi"></a></h3>
<p>The Data Documentation Initiative standards are produced and
maintained by a member-based consortium of global scope, the
<a href="http://www.ddi-alliance.org/">DDI Alliance</a>. Housed
currently at the
<a href="http://www.icpsr.umich.edu/">Interuniversity Consortium
for Political and Social Research</a> (ICPSR) at the University
of Michigan, there are currently more than 30 member
institutions. The standards have been under development for more
than ten years, and are in widespread use among data archives
and libraries, producers of research data, secure data centers,
and statistical agencies.</p>
<p>There are two major versions of DDI (both serialied in XML format): the
“<a href="http://www.ddialliance.org/Specification/DDI-Codebook/">Codebook</a>”
version, which allows for holding general information
about a study, along with its data dictionary; and the
“<a href="http://www.ddialliance.org/Specification/DDI-Lifecycle/">Lifecycle</a>”
version of DDI, which allows for the description of more complex
multi-wave studies, throughout the data lifecycle, from study
conception through data collection and processing.</p>
<p>This vocabulary contains a selection of the major types of metadata defined by these two versions in a highly simplified form, for the purposes of discovery. The XML
Codebook and Lifecycle versions of DDI are very broad: these
standards contain hundreds of metadata elements, providing
enough information to programmatically work with the data files
for such functions as the automatic creation of databases, and
transformations between statistical packages. DDI in both
versions is generally used to describe data found in ASCII
files, whether positional files with fixed-width fields or files
using a delimited format such as CSV.</p>
<p>It is difficult to claim that there is a single agreed
conceptual model for describing research data in the social,
behavioural, and economic sciences—there is a wide range of
models and terms. However, the issues faced in this area have
been the subject of discussion within the DDI community for many
years, and the DDI model represents the best consensus which
exists today. As such, it gives us a good basis for creating a
vocabulary which will be recognizable to researchers familiar
with this type of data.</p>
</section>
<section id="relationship-to-data-cube-dcat-and-xkos">
<h3 id="x2-3-relationship-to-data-cube-dcat-and-xkos"><span class="secno">2.3 </span>Relationship to Data Cube, DCAT and XKOS<a class="self-link" aria-label="§" href="#relationship-to-data-cube-dcat-and-xkos"></a></h3>
<p>The Discovery Vocabulary (Disco) is aligned to several other metadata
vocabularies used in the RDF community. Disco is designed to be used in conjunction with other vocaularies.</p>
<p>The <a href="http://www.w3.org/TR/vocab-dcat/">Data Catalog
Vocabulary</a> (DCAT) is a <abbr title="World Wide Web Consortium">W3C</abbr> standard for describing catalogs
of datasets, and we map to it in two places:
Our <code><a href="#dfn-disco-logicaldataset" class="internalDFN">LogicalDataSet</a></code> is a subclass of DCAT’s Dataset, and our
<code><a href="#dfn-disco-datafile" class="internalDFN">DataFile</a></code> is a subclass of DCAT’s Distribution. DCAT makes few
assumptions about the kind of datasets being described,
and focuses on general metadata about the datasets
(mostly using Dublin Core), and on different ways of
distributing and accessing the dataset, including availability
of the dataset in multiple formats. Combining terms from both
DCAT and the Discovery Vocabulary can be useful for a number of
reasons:</p>
<ul>
<li>Describing collections (catalogs) of research datasets (DCAT)</li>
<li>Providing additional information about physical aspects (file size, file formats) of research data files (DCAT)</li>
<li>Providing information about the data collection that produced the datasets in a data catalog (Disco)</li>
<li>Providing information about the logical structure (variables, concepts, etc.) of tabular datasets in a data catalog (Disco)</li>
</ul>
<p>DCAT is richer for the description of collections and catalogue. Disco supports richer descriptions of groups of datasets or individual datasets. In this spec, some of our examples are partially based on DCAT (and we will indicate when this is the case).</p>
<p>The <a href="http://www.w3.org/TR/vocab-data-cube/">Data Cube
vocabulary</a> is a <abbr title="World Wide Web Consortium">W3C</abbr> standard for representing data cubes,
that is, multidimensional aggregate data. Data cubes are often
generated by tabulating or aggregating record-level datasets.
For example, if an observation in a census data cube indicates
the population of a certain age group in a certain region is
12345, then this fact was obtained by aggregating that number of
individual records from a record-level (or “microdata”) dataset.
The Discovery Vocabulary contains a property “aggregation” (pointing from a Disco data set to a Data Cube dataset) that
indicates that a Cube dataset was derived by tabulating a
record-level dataset.</p>
<p>Data Cube provides for the description of the structure of
such cubes, but also for the representation of the cube data
itself, that is, the observations that make up the cube dataset.
This is not the case for the Discovery Vocabulary, which
only describes the structure of a dataset, but is not concerned
with representing the actual data in it. The actual data is
assumed to sit in a data file (e.g., a CSV file, or in a
proprietary statistics package file format) that is not represented
in RDF.</p>
<p>
The interplay of Data Cube and Disco needs further exploration regarding the relationship of aggregate data,
aggregation methods, and the underlying microdata.
The goal would be to drill down to the related microdata based on a search resulting in aggregate data.
On the one hand aggregate data are often easily available and gives a quick overview.
On the other hand microdata enable more detailed analyses.
</p>
<p>The use of formal statistical classifications is very common
in research data sets—these are treated in our vocabulary as
SKOS concepts, but in some cases those working with formal
statistical classifications may desire more expressive
capability than SKOS provides. To support such users, the DDI
Alliance also publishes
<a href="http://purl.org/linked-data/xkos">XKOS</a>, a
vocabulary which extends SKOS
to allow for a more complete description of such
classifications. While the use of XKOS is not required by this
vocabulary, the two are designed to work in complementary fashion.</p>
<p>More details on the relationship to Data Cube, DCAT and XKOS as well as to other vocabularies are provided in Section 9.</p>
</section>
</section>
<section id="overview">
<!--OddPage--><h2 id="x3-overview"><span class="secno">3. </span>Overview<a class="self-link" aria-label="§" href="#overview"></a></h2>
<!-- <div class="figure">
<img class="uml-diagram" src="diagrams/overview.png" alt="Vocabulary Overview"/>
</div>
-->
<figure id="fig-vocabulary-overview">
<img class="uml-diagram" src="diagrams/overview.png" height="964" width="1440" style="width: 792px;">
<figcaption>Figure <span class="figno">1</span> <span class="fig-title">Vocabulary Overview</span></figcaption>
</figure>
<p>To understand the DDI Discovery Vocabulary, there are a few
central classes, which can serve as entry points. The first of
these is the <code><a href="#dfn-disco-study" class="internalDFN">Study</a></code> class. A <b><code><a href="#dfn-disco-study" class="internalDFN">Study</a></code></b> in our model represents the
process by which a data set was generated or collected. Literal
properties include information about the funding, organizational
affiliation, abstract, title, version, and other such high-level