CRANV1P1 Indexing Procedures chapter Cyril Cleverdon Jack Mills Michael Keen Cranfield An investigation supported by a grant to Aslib by the National Science Foundation. Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. 42 - 2. precision devices - those which, applied to any existing class, decrease the size; e.g., if we coordinate Bakelite with Extrusion and examine only the class defined by this simple relationship of intersection, we exclude those documents on Bakelite which do not refer specifically to this operation. The operation of these devices on the sort of simple index description described above can be seen by a consideration of the relations such a description displays to the precise subject of the document concerned, and to the wider subject field of the information store from which we may wish to retrieve that document or some- thing like it. An index description a, b, c, d, e, f (where each letter represents a substantive term or lexical element, e.g., Wing, Drag, Control) embodies two sets of relations: firstly, those internal to it, reflecting the local and temporary conditions peculiar to the subject of the document described; e.g., the fact that dis the product, whereas f is an agent of the process a which produces it, or, the fact that b qualifies a while c qualifies d, but that neither of these qualifiers is applicable to the object of the other; or, more subjectively, that a_ and b, rather than c d e or f, represent the domi- nant theme of the document. These are, broadly speaking, the interlocking relations between the substantive terms. The second set of relations are those external to it, reflecting the more perman- ent pattern of relations in the wider field or subject area to which the document belongs: e.g. , that a is a species of x, or that c is almost synonymous with q_, or that a represents one participle of a term (e. g.[OCRerr] Cooling) which may be usefully related to another participle (e. g. Cooled) in the subject concerned. The two sets of relations can be utilized to add precision to the original des- cription (using the first set) or to expand the description by reference to the wider relations (using the second set}. In other words, they underlie the two groups of index language devices which will now be outlined briefly. Devices which increase precision (i) Coordination - i. e., the conjunction of two or more terms to produce a nar- rower class defined by the intersection; e.g. Shear and Flow to give Shear flow. This is the most important device in indexing. Whilst it is commonly associated with postcoordinate systems where it is implemented mainly if not entirely at the search stage, it is equally fundamental to precoordinate systems; but in these, only the products of selected coordinations are usually catered for conveniently. (ii) Weighting - i. e., the assignment to a term of a figure representing the relative significance of that term in the total subject description of the document. So a term which represents the central theme of the document gets a high weighting and one which represents only a marginal element in the subject content of the document gets a low weighting. If now a question is also weighted, i.e., greater significance attaches to one or some of its terms than to others, then the search may be directed only to coordinations with that term or only to the same term when it has been given a similarly high value in indexing. In either case, the class of documents retrieved is made narrower. (iii) Links - i. e., indicating a particular connection between two or more terms in a description where the lack of such an indication would produce ambiguity; e.g., if the same document deals with the hardness of copper and conductivity of titanium a link between Hardness and Copper on the one hand and between Conductivity and