In scientific information, then, we find that subjects - the themes and topics on which books and articles are written - cluster into fields, each of which can be analysed into its characteristic set of facets of terms.

— Brian Campbell Vickery, Classification and indexing in science (1958)

Source: http://jenserikmai.info/Papers/2010_Classificationinasocialworld.pdf

From the first chapter of his 1958 book.

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