In order to avoid some of the aforementioned drawbacks concerning subject-based information retrieval, thesauri have been employed ([1], [11]). When used during retrieval and searching, thesauri are useful in bridging the gap that exists between the metadata provided by the indexer and the concepts presented by a searcher [3]. Moreover, thesauri can be employed to promote guided and/or faceted navigation by exploiting the semantic structure between their underlying terms [4]. Such navigation ultimately results in query construction for queries addressed to the underlying search engine.
Despite their inherent drawbacks (addressed in Bechhofer and Goble [4]), thesauri have proved to be quite effective for information discovery using print tools. However, due to the fact that their semantic structure is less well deployed for users in online settings, the impact of thesauri in subject-based information retrieval is less than expected in those settings. Schwartz [13] provides an extensive, annotated overview of recent research in thesauri-based information retrieval. Following this research, it could be stated that ontology-based systems seem capable of addressing many of the problems concerning the modeling of the semantic structure within thesauri, thus leading to the development of more effective subject-based information retrieval systems.
Thinking along this line, a thesauri-related system that could potentially be applied to serve LCSHs is ONKI-SKOS [6]. The ONKI-SKOS server provides a uniform way of accessing thesauri represented as Simple Knowledge Organization System - SKOS3 vocabularies. As far as the user interface is concerned, the ONKI-SKOS server provides an auto-suggest function that acts as an entry point for the entire thesauri-based information retrieval process. Then, users are provided with a hyperlink-based interface to traverse the thesaurus, which is encoded in OWL format. ONKI-SKOS can be used to browse, search and visualize any vocabulary that conforms to the SKOS specification. ONKI-SKOS thesauri are capable of representing basic SKOS relations between concepts such as hierarchical relations and synonyms.