Knowledge organization systems such as thesauri or taxonomies are increasingly being expressed using the Simple Knowledge Organization System (SKOS) and published as structured data on the Web. Search engines can exploit these vocabularies and improve search by expanding terms at query or document indexing time. We propose a SKOS-based term expansion and scoring technique that leverages labels and semantic relationships of SKOS concept definitions. We also implemented this technique for Apache Lucene and Solr. Experiments with the Medical Subject Headings vocabulary and an early evaluation with Library of Congress Subject Headings indicated gains in precision when using SKOS-based expansion compared to pseudo relevance feedback and no expansion. Our findings are important for publishers and consumer of Web vocabularies who want to use them for improving search over Web documents.

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