A thesaurus is a controlled and structured vocabulary where concepts are represented by Preferred Terms. Preferred Terms are used for keyword annotation purposes. Optionally, one or more alternative labels or Entry Terms can be linked to a Preferred Term. Entry Terms are typically synonyms or near-synonyms of Preferred Terms, and are not used for keyword annotation, but lead the user to the Preferred Term in question.
Each concept in HASSET is identified by a dereferenceable Uniform Resource Identifier (URI) (= URL).
Each concept of the thesaurus can be semantically related to other concepts within the thesaurus. Hierarchical relations are represented by Broader Concepts and Narrower Concepts, while non-hierarchical associative relations are represented by Related Concepts.
HASSET concepts may also be associated with different types of note field: Definition, Definition Source, Scope Note, and History Note. A Definition describes the meaning of the concept within the thesaurus, while a Scope Note provides advice on term usage to either indexers or searchers. A Scope Note may also clarify the meaning of the concept with respect to other concepts in the thesaurus. A History Note records the date of introduction or the changes made to an existing term. A full list of Definition Sources can be found in the Bibliography of Definition Sources.