Although concept systems and thesauri can both be used to represent information and knowledge, concept systems are used to represent concept structures in terminology and information management, whereas thesauri are constructed specifically for information retrieval purposes in library science and documentation environments. The two traditions are subject to different conventions and rules and would not normally be combined. Nevertheless, a terminological entry can indicate that a term is a thesaurus descriptor in a documentary language. A number used to represent concept position or the position of a thesaurus descriptor is frequently called a notation.