SKOS for topical systems. The SKOS data vocabulary is meant to express knowledge organization systems. Examples of such systems, according to its specification, are “thesauri, taxonomies, classification schemes and subject heading systems”.40 These systems have a number of traits in common — traits that can be expressed in SKOS in order to bring such knowledge to the Semantic Web environment. The terminology in SKOS revolves around the notion of concepts. The definition of the term Concept is “a unit of thought”, a rather general notion 38See the properties iso-thes:broaderGeneric, iso-thes:broaderInstantial, iso-thes:broaderPartitive, which are asserted to be subproperties of skos:broader. 39LOV, s.v. ‘ontopic’. 40‘SKOS Simple Knowledge Organization System Reference’. that ensures wide support for informal organizing systems.41 Such systems all express and organize items, and SKOS therefore includes terminology to organize concepts into informal hierarchies (using the relations broader and narrower between concepts) and to create cross-references between concepts (using the relation related). The concepts themselves can be described using labels and notes, and aggregated into collections (Collection) and schemes 117 (ConceptScheme). The terminology available in SKOS is expressive enough to capture the majority of the information found in the topical system of historical language thesauri. Each category can be represented as a concept in SKOS, identified by its own IRI, labelled with a name, and placed in an informal hierarchy. The identification of a category, which encodes the position of a category within the topical system, can be expressed using the SKOS notation property. These identifications are, in historical language thesauri, sufficient to deduce the order of co-ordinate categories when presenting them. Editorial commentaries, too, can be expressed in SKOS through its system of notes. In short, the coverage of this data vocabulary is extensive and warrants an assessment to determine whether SKOS is sufficiently standardized, too, for representing historical language thesauri. SKOS was finalized and published in 2009 as a recommended standard by W3C, the consortium that initiated and maintains the technological specifications for the Semantic Web. As such, SKOS is backed by an authoritative body in the Semantic Web community. The quality of the vocabulary is perhaps best illustrated through its use and reuse. As Figure 3.1 shows, SKOS has certainly seen reuse and speciali...
