"It can be useful to distinguish between knowledge and information and data; it is also difficult and contentious. Four points should be made. [First] Knowledge, information and data is what the systems to be discussed are for: by storing it in an organized manner, they are intended to enable it to be found when needed. Secondly, there is a spectrum of increased size and organization between data, where the units are quite small, through to knowledge, where the units are large and distinguished by their complex internal structure and relationships, and overlap with other units... Meunier (1987) presents a typology of levels of representation which is useful for the breath of its approach and its classification of relationships. Thirdly, "information" in the expression "information retrieval" is generally abused, because what is retrieved is not information, but bibliographic details of sources in which desired information potentially exists. Very many information retrieval systems are at best document retrieval systems, and more usually they are systems which retrieve surrogates for documents... Finally, although the expression knowledge retrieval is particularly associated with artificial intelligence and expert systems, it should not be forgotten that this is what cataloguers, indexers and bibliographers have been doing, and devising systems for, for many years."