[1] In automatic classification it could be the number of times given words appears in a document.
In this way it is not necessarily a kind of classification or indexing based on user studies.
Only if empirical data about use or users are applied should request-oriented classification be regarded as a user-based approach.
Sometimes a distinction is made between assigning documents to classes ("classification") versus assigning subjects to documents ("subject indexing") but as Frederick Wilfrid Lancaster has argued, this distinction is not fruitful.
The view that this distinction is purely superficial is also supported by the fact that a classification system may be transformed into a thesaurus and vice versa (cf., Aitchison, 1986,[4] 2004;[5] Broughton, 2008;[6] Riesthuis & Bliedung, 1991[7]).