has been compiled. A subject specialist is consulted before new
keywords are added to the system.
3.7 Control of Terminology
3.7.1 The efficiency of the control and manipulation of ter
minology is fundamental to the systems described in the preceding
paragraphs. To replace the logical structure of a classification
scheme, which shows relations between subjects, cross-references
must be introduced. In some subject fields, highly-developed sub
ject lists, known as thesauri, have been produced. A typical extract
from the American 'Engineers Joint Council Thesaurus' is shown
below
Density
UF Gravity
relative density
specific gravity
specific weight
NT bulk density
theoretical density
BT physical properties
RT bulk modulus
buoyancy
density measurement
porosity
void ratio
UF (use for) are terms not used in the index, treated as synonyms
of density, NT terms are narrower (more specific) than the general
term 'Density', and BT are broader (more general). The RT (related)
terms refer to other index entries that a searcher may find it useful
to follow up in a generic search.
3.7.2 This Thesaurus is considered to have two functions
to permit the indexer to describe more fully and at different levels
of generality and from many technical points of view, the infor
mation contained in documents, and to permit the searcher for
information to phrase an inquiry appropriate to the scope and
degree of his immediate interests employing all the terms of the
retrieval vocabulary which have appropriate meaning and specificity.
3.7.3 The School of Library Science, Western Reserve University,
USA, has established, with the aid of a UNESCO grant, a clearing
house for scientific and classification schedules. Keyword and
descriptor lists and thesauri in the English language have been
issued, to assist individuals and organisations in their scientific
and technical information retrieval problems.
3.8 Geodetic Thesaurus
3.8.1 Although there has been established recently for geodesy
and related fields (photogrammetry, cartography), a new UDC-
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