AUTOMATIC INDEXING
A State-of-the-Art Report
Mary Elizabeth Stevens
A state-of-the-art survey of automatic indexing systems
and experiments has been conducted by the Research Information Center and Advisory Service on Information Processing,Information Technology Division, Institute for Applied Technology, National Bureau of Standards. Consideration is firstgiven to indexes compiled by or with the aid of machines,
including citation indexes. Automatic derivative indexing is
exemplified by key-word-in-context (KWIC) and other wordin-context techniques. Advantages, disadvantages, and p o s s i bilities for modification and improvement are discussed.
Experiments in automatic assignment indexing are summarized.
Related research efforts in such areas as automatic classification and categorization, computer use of thesauri, statisticalassociation techniques, and linguistic data processing aredescribed. A major question is that of evaluation, particularly
in view of evidence of human inter-indexer inconsistency. It
is concluded that indexes based on words extracted from text
are practical for many purposes today, and that automatic
assignment indexing and classification experiments showpromise for future progress.
1.

INTRODUCTION

This report of the Research Information Center and Advisory Service on Information
Processing (RICASIP) A/ is one of a series intended as contributions to improved cooperation in the fields of information selection systems development, information r e trieval research and mechanized translation. In each of these areas, automatic techniques for linguistic data processing are receiving increased attention. This reportcovers a state-of-the-art survey of current progress in linguistic data processing as
related to the possibilities of automatic mechanized indexing. Insofar as has beenpractical, the survey of the literature on which this report is based has been madethrough February 1964.
It has concentrated on the major developments in and related demonstrations of automatic indexing potentialities. Examples are also given of indexes compiled by machineand of potentially related research efforts in such areas as natural language text searching, statistical association techniques used for search and retrieval, and proposedsystems for concept processing. There are, undoubtedly, various omissions. Neither
the inclusion of reports on various specific experiments and techniques nor the omissionof others is intended to reflect an endorsement as such of those that are included or anadverse evaluation of those that are not mentioned.

y
Initiated at the instigation of the National Science Foundation.
supported by NSF and NBS.

1

RICASIP is jointly

1. 1 Definitions and BackgroundThe noun "index11 has as its most general meaning "something used or serving topoint out, a sign, token, or indication", (American College Dictionary) or "that whichshows, indicates, manifests, or discloses; a token or indication" (Webster's International
Dictionary, 2nd Edition, unabridged). More specifically, an index is "a pointer or key
which directs the searcher to recorded information1.—' The terms "index" and "indexing"
have been used in the fields of library science and documentation with reference to the factthat the selection of information pertinent to a particular problem or interest, from all thepreviously recorded information available, involves problems of decision-making basedon l e s s than the full content or text of each of the records being searched.
Short of complete scanning of all the possibly relevant material, it is necessary to
select or "distill" condensed representations or surrogates f*/ for each item. Thesesurrogates are intended to direct the searcher to the most probably pertinent items in acollection. The operations known as "indexing" thus involve:(1)

Choosing clues that will serve to identify, for purposes of later retrieval, aparticular book, document, or other recorded item, and(2)

Either marking on the item itself or recording as a separate item-surrogate
the tags, labels, or codes representing these clues.

The second of these two steps can be purely clerical in nature, but the first has been,
to date, primarily the result of human intellectual efforts in subject content analysis.
Well-known inadequacies of human indexing operations include both those stemmingfrom man himself and those which result from the volume and the character of thematerials with which he deals. On the human side, there are fundamental questions ofperception, comprehension and judgment, as well as those of inter-indexer and even intraindexer consistency. In addition, the indexer is asked to guess in advance what others
will ask for, understand, and find relevant on future search. He is even asked, in effect,
to anticipate the language of future inquiries. Thus, a somewhat facetious definition of thenoun "index" has a considerable sting of truth: "A system of analyzing information inwhich the method used to choose categories i s carefully hidden from the user. An attempt
to outguess the future. "The nature of the material to be indexed, especially in the area of scientific information, raises a number of crucial problems. The still increasing spate of production oftechnical literature and reports poses not only the problems of sheer volume in terms ofu
Crane and Bernier, 1958 [ 1 4 4 ] , p. 513.
(Note: Full citations of references are given in the bibliography by author and bynumerical order of the figures in brackets. )USee, for example, R. E.Wyllys, 1962 [ 6 5 l ] , for discussion of the two-fold purposesof condensed representations: to serve a search-tool function on the one hand anda content-revealing one on the other.
Vanby, 1963 [ 6 2 2 ] , p. 143.

2

manpower requirements and time necessary to produce indexes, but also problems of glutin terms of man-hours necessary for the individual scientist to maintain awareness ofwhat is going on in his field. There are major problems created by newly emerging fields
of effort, new interdisciplinary areas of interest, and dynamically evolving terminology.
Increasing specialization, on the other hand, brings out additional difficulties in finding
what has been done elsewhere that might be applicable to one's own work and in avoiding
wasteful duplication of effort, with their own attendant problems of terminology.
All these problems are aggravated by the increasingly critical urgency which should
apply to making all useful information available to those who need it as promptly and as
selectively as possible. Recognition of this urgency and of the inadequacies of present
solutions has therefore prompted consideration of the feasibility of using machines toa s s i s t in the indexing process.
The term "mechanized indexing" signifies the accomplishment of some or all of theindexing operations by mechanized means. The term includes the use of machines toprepare and compile indexes, and to sort, assemble, duplicate and interfile catalog cards
carrying index entries. In this report, however, we shall be concerned primarily withthe area of automatic indexing, that i s , the use of machines to extract or assign index
terms without human intervention once programs or procedural rules have been established. This term is chosen in preference to auto-indexing as originally suggested by .
Luhn (1961 [ 373]) for the reasons set forth by Bar-Hillel, i / and to machine indexing —due to possible confusion with machine tool operations. Automatic indexing has been usedby such workers in the field as Gardin (1963 [209]), Kennedy (1962 [310]), Maron (1961[395]), Swanson (1962 [584]), and Wyllys (1963 [ 6 5 3 ] ) .
For obvious reasons, we also subsume under this term any specifically "clerical"(Fairthorne, 1956 [ 1 8 8 ] , 1956 [ 1 8 9 ] , 1961 [ 190] and hence machinable operations thatcan similarly be substituted for human intellectual effort. There is nothing that machines
can do which people cannot do except for limitations of time, cost, or availability of
appropriate resources. Thus, we shall consider "machine-like indexing by people"(O'Connor, 1961 [447]; Montgomery and Swanson, 1962 [421]) as falling properly within
the scope of automatic indexing, especially in the sense of ". . . deciding in a mechanicalway to which category (subject or field of knowledge) a given document belongs . . . deciding automatically what a given document is 'about1. " 2 /The principle of indexing, that i s , of using subject-content clues and item surrogatesas substitutes for searches based on perusal of the full contents, has a history of several
millenia. In ancient Sumaria and Babylon, clay tablets were sometimes covered with athin clay envelope or sheath that was inscribed with brief descriptions of the contents ofthe tablet itself (Carlson, 1963 [ 1 0 1 ] ; Hessel, 1955 [268]; Lalley 1962 [ 3 4 3 ] ; Olney,
1963 [ 4 5 8 ] ; Schullian, I960 [ 5 2 5 ] ) . The first known instance of an index list isapparently that of Callimachus in the third century B. C. , which was a guide to the contents of some 130,000 papyrus rolls (Olney, 1963 [458]; Parsons, 1952[469]).

U
Bar-Hillel, 1962 [ 3 5 ] , p. 417.

liBohnert, 1962[693; Edmundson, 1959 [ 1 7 6 ] ; and others.

I!
Maron, 1961 [ 3 9 5 ] , p. 404.

3

Application of the indexing principle by use of clerical procedures that today can beaccomplished by machine was suggested a little more than a century ago. A British
librarian, Andreas Grestadoro, advocated the permutation of the words in titles in 1856,
claiming that thus the subject matter index would follow the author's own definition of thecontents of his book. He prepared such f 'concordances of titles" for several different
library collections. A/
Within a generation, punched card machines had been invented, but they were not to
be used for library and documentation purposes for some decades yet. £ / Keppel,
writing in 1937 of his vision of the library 21 years in the future, says:"When it comes to using the cards, I blush to think for how many years we watched
the so-called business machines juggle with payrolls and bank books before it
occurred to us that they might be adapted to dealing with library cards with equal
dexterity. Indexing has become an entirely new art. The modern index is nolonger bound up in the volume, but remains on cards, and the modern version of
the Hollerith machine will sort out and photograph anything the dial tells it . ..
"3/
By 1945, Bush had prophesied M e m e x [ 9 3 ] , and in the 1950 Windsor lectures
Ridenour referred to an RCA development, the so-called "electronic pencil", a proposed
reading aid for the blind intended to convert printed characters to a suitable coded form.
He went on to suggest:" . . . We shall have to arrange for cataloguing to be done by machine, without
human interaction except in terms of setting up once for all the system on
which the cataloguing is performed.. . It is only a step from this device (theelectronic pencil) to the electronic catalogue, which will read text for itself,
recognize key symbols and phrases with which it has been provided, and construct appropriate catalog entries for the text it reads."$J
It has only been in the past decade or so, however, that there have been any serious
efforts directed to the use of machines for automatic indexing. In the period 1957-1958,
Luhn first presented and published several provocative papers dealing with suchchallenging possibilities as "auto-abstracting", "auto-encoding" and "auto-indexing"(Luhn, 1957 [ 3 8 5 ] ; 1958 [374]; 1959 [ 3 7 l ] ). Luhn's work on the permutation of significant words in titles, abstracts, and complete text, the Keyword-in-Context or KWIC

1/
See Crestadoro, 1856 [ 1 4 6 ] ; see also Farley, 1963 [ 1 9 2 ] ; Linder, I960 [362];
Metcalfe, 1957 [ 4 1 6 ] ; and Ohlman, 1 9 6 0 [ 4 5 l ] .

y
See pp.19-22 of this report.

y
See Keppel, 1939 [316], p. 5.

±1
See Ridenour, 1951 [ 5 0 0 ] , p. 26.

4

system, also began about this time. — A l i o in 1958, Baxendale published the results ofexperiments in automatic indexing involving scanning of topic sentences, syntacticaldeletion p r o c e s s e s and automatic phrase'selection (Baxendale, 1958 [ 4 1 ] ).
With respect to the KWIC and permuted title techniques, several independent
approaches were being developed at about the same time as Luhn f s. These concurrent
efforts were carried out at the Wright Air Development Center (Netherwood, 1958 [437])ithe Rocketdyne Division of North American Aviation (Carlsen, et al, 1958 [ 9 9 ] ) , and the
System Development Corporation (Citron, et al 1958 [ 1 2 0 ] ; Ohlman, I960 [ 4 5 l ] ) . ? i
Netherwood f s permuted title index to a bibliography on logical machine design involves
manual simulation of a machineable method. Although the results were not publisheduntil June 1958, the manuscript was submitted in November 1957.—' The Rocketdyne
permuted-title bibliography, on industrial control, is credited by both Henderson (1962[ 2 6 3 ] ) and Ohlman (I960 [ 4 5 1 ] ) as the first to be produced on computers, the program1/

In a private communication dated March 13, 1963, Luhn provided the following
chronology:
May 1957

Routine 1 Program for word isolation within 60 characters per card,
written by H. C. Fallon.

1957-1958

Creation of concordances of various scientific papers in the form ofcards, each card showing a keyword centrally located within 60 lettersworth of the associated phrase. Experimentation with these cards toarrive at thesauri for special fields of interest or study. Idea of automatic indexing by means of significant or keywords in context conceived
by H. P. Luhn.

May 1958

Keyword-in-Context Index for titles only initiated by H. P. Luhn andsamples produced with Routine 1 Program.

June 1958

Start punching of titles for Keyword-in-Context Index for literature on
Information Retrieval and Machine Translation. (Keypunching done byMiss Olive Ferguson.)August 1958

Simplified version of Routine 1 written by H. C. Fallon for generating
Keywords-in-Context Indexes and delivered to Service Bureau
Corporation, New York City.

September
1958

First Fdition of Bibliography and Keyword-in-Context Index on
Information Retrieval and Machine Translation published by Service
Bureau Corporation.

January 1959 Started writing program for improved version of Keyword-in-Context
Index, including derived identification code, written by Jr. J. Havender.
June 1959

Second Edition of Bibliography and Keyword-in-Context Index on
Information Retrieval and Machine Translation, published by Service
Bureau Corporation, including derived identification codes.

2/

See also National Science Foundation's CR&D Report No. 3, [ 4 3 0 ] , p. 39.
U

Netherwood, 1958 [437] , p. 155, footnote.
5having been written by J. T. Madigan. — At any rate, both this program and Luhn's
KWIC program at IBM were apparently written relatively early in 1958.
Citron et al (1958 [ 120] ) in presenting results of the SDC work and Ohlman in his
chronological bibliography of permutation indexing (I960 [ 4 5 l ] ) c i t e as at least partial
predecessors the "rotated file" principles developed at the Chemical-Biological Coordination Center (1954 [ 1 1 2 ] ; Heumann and Dale, 1957 [ 2 7 0 ] and 1957 [ 2 7 1 ] ; Wood, 1956
[ 649] ). It should also be noted as a matter of historical background that a system formachine manipulation and compilation of permuted title-and-term-index records has beenin productive operation since 1952. U This earlier effort was not generally known toother investigators and was apparently first reported in the open literature as late as 1961.
Notwithstanding such other efforts, it is conceded by almost all workers in the fields
of automatic abstracting and indexing that the major credit for pioneering interest and
impetus should be attributed to Luhn and Baxendale. Specific acknowledgements of their"pioneering work" and "first steps" have been made by many investigators both in thiscountry and abroad--for example, Borko and Bernick, —'Hines, Z' Mooers, —' Pevzner
and Styazhkin, —' and Wyllys.Z' In particular, the Russian investigator Purto states:"So far as we know H. P. Luhn was the first investigator to suggest the concept of a setof significant words for the consideration of problems in automatic abstracting. "Much of the early effort 1957-58, whether at IBM or elsewhere, was in fact spurred
on by the International Conference on Scientific Information (ICSI) held in Washington, D. C. ,in November, 1958. The printed text of both the Preprints [478] and the final
Proceedings [480, 481] was deliberately prepared, over the typographer's objections,so that a double space followed each period ending a sentence, in order to facilitate
machine processing of this text. Thus the printers "• . . . were faced with . . . thenecessity to prepare the final volume of the Proceedings from these preprints, and toarrange type composition amenable to computer analysis. The latter is an experiment.
With an eye to the distant future, the Program Committee wished to make available themonotype punched tapes from the text for statistical studies with computers. We hopeU
Carlsen, et al, "Information Control", 1958 [ 9 9 ] , p. 20.

U
Veilleux, 1962 [ 624] , p. 81: "Consumer demand balanced against availability of man
power and machine time were the factors which led to the establishment of the permutation title word indexing project in 1952. "U
Borko and Bernick, 1962 [77] , p. 3.
4/Hines, 1963 [273 j , p 7.

SJ Mooers, 1963 L424] , p. 4.
6/

Pevzner and Styazhkin, 1961 [472] , p. 3.

7/

Wyllys, 1961 [ 6 5 0 ] , pp. 6-7.

8/

Purto, 1962 [ 4 8 4 ] , p. 2.

6some work of this kind will be demonstrated during the Conference,compromises in typography... ''W

This has caused some

Several pibneering experiments in automatic indexing were applied to this ICSI
material. One of these led to the preparation of a permuted keyword index based on
titles, subtitles, section and table headings, figure captions, and selected sentences orphrases taken directly from the text (Citron, et al, 1958 [ 1 2 0 ] ) . It was prepared using
punched card equipment, arid the resulting listings were distributed to the Conference
participants in November of 1958. Another set of experiments involved trial of the "autoabstracting" and "auto-encoding" techniques proposed by Luhn (1958 [ 379] ).J— A
computer program potentially applicable to certain ancillary operations which might beinvolved in automatic indexing was also demonstrated at the time of the ICSI s e s s i o n s .
(Stevens, 1959 [568] ).
Much of the rapidly proliferating work in the field of automatic indexing since thattime has been inspired directly or indirectly by the results of these experiments using
the ICSI material. For example, Dow ell and Marshall, discussing early efforts at the
English Electric Company, state: "We first became interested in the possibilities ofcomputer produced indexes through Luhn f s work at IBM and the early examples of KWIC
indexes which were distributed at the time of the Washington Conference. . . " (Dowell
and Marshall, 1962 [159] ) . - 'y"Preprints of papers of the International Conference on Scientific Information, "1958, [478], Preface. (The monotype tapes are in fact still held in the custody of
the Research Information Center and Advisory Service on Information Processing,
National Bureau of Standards, but difficulties to be discussed later in this reportdiscourage their u s e . )y
See also his "Automated intelligence systems" 1962 [ 3 7 2 ] , note. 11, p. 100:
"Papers for this conference were distributed to participants two months ahead forstudy. By arrangement with the Columbia University P r e s s the Monotype tapes usedin publishing these preprints were made available for experimentation. At theconference exhibit, IBM researchers demonstrated the automatic transcription ofthese Monotype tapes to magnetic tape via punched cards and thence the automatic
creation and printout of abstracts by means of electronic data processing equipment
at the Space Systems Center in Washington, D. C. All this was done without any
human intervention except for the handling of the input and output records. Also,
preprinted Auto-Abstracts of Papers of Area 5 of the Conference were made available to participants at the beginning of the conference."

If
See also R. A. Kennedy, 1962 [310]> p. 181: "While automatic indexing in any
interpretative and analytical sense is therefore not yet a practical matter, a
simpler mode of machine indexing i s coming into wide use . . . primarily
stimulated by the publication in 1958 and 1959 of reports by Ohlman; Hart andCitron and Luhn. "7

A somewhat premature attempt was made to establish a subscription service for
KWIC indexes for a number of journals, for initial distribution beginning January 1,
1959. L' Called PILOT (Permutation Indexed Literature Of Technology), the proposedservice was advertized as !, a revolutionary new totally cross-referenced index . . . and it
will be produced at the speed of light 1 '. Figure 1 is a reproduction of a part of thebrochure issued in 1958 by Permutation Indexing, Incorporated, Sol Grossman, President,
Los Angeles. While, perhaps unfortunately, the number of subscription orders received
was not adequate in terms of the ambitious coverage planned, work on permuted title
indexing elsewhere did lead rapidly to the publication of such indexes on a production
basis.
As of February 1964, there are more than04O examples of KWIC and other variationsof permuted keyword indexing techniques in productive operation or available to thesearcher. KWIC-type techniques have also been extended to special one-time index compilations and other applications, as in "automated content analysis" of verbal protocols of
psychiatric interviews and group leadership training sessions (Ford, 1963 [ 198]; Hart andBach, 1959 [ 2 5 6 ] ; Jaffe
1962 [294] and 1958 [ 2 9 6 ] ; Stone, et al, 1962 [575] ).
The same period during which the ICSI was planned and held (1957-1958) was also
marked by the first issue of Current Research and Development in Scientific Documentation by the National Science Foundation. In it and in subsequent i s s u e s , there werereported other early efforts in machine-compiled indexes, in the construction and use of
special thesauri, and in indexing and retrieval experiments based on machine processingof text. Thus, for example, punched card methods for compiling printed indexes andannouncement lists were under consideration at Bell Laboratories and at E s s o Researchand Engineering. Special attention was being given to thesauri as early as July 1957 atboth Chemical Abstracts Service and the Cambridge Language Research Unit, andat Ramo Wooldridge, "Research on the problems of fully automatic indexing and retrieval
based on raw text input to a general-purpose computer is under way. "2/
Nevertheless, as of the present date, the question of the possibility of automatic
indexing in the sense of the substitution of machineable procedures for human intellectual
efforts normally required to identify, categorize, classify, index, select, and list
particular items in a collection of items is still moot. Opinions run the gamut fromextreme p e s s i m i s m , "Mechanization of abstracting and indexing is rejected as impractical for the foreseeable future"i/to enthusiastic optimism, "The conclusion that automatic
indexing and cataloging is superior to human indexing and cataloging is both provocativeand remarkable. " 1 /Borko and Bernick claim that " . . . Raw data, i. e . , unedited natural language text,
can be processed statistically so as to automatically assign index terms to each document
and to classify the document into a subject category; this has been demonstrated. " kl On
the other hand, Farradane thinks that any form of mechanized processing in indexingU
See Linder, I960 [ 3 6 3 ] , p. 99 and Figure 1.

II
National Science Foundations CR&D Reports No. 1, [430]pp. 4 , 6 ; No. 3 [430] ,pp. 12, 19, 31.
3/—

Bar-Hillel, 1958 [33] , abstract.

1/

Swanson, 1962 [584] , p. 468.

5_/

Borko and-Rernick, 1963 [ 7 8 ] , p. 28.
8

If

s
THE PRINCIPLE OF PILOT'S PERMUTATION INDEXING CAN BE DEMONSTRATED BY ONE SAMPLE TITLE:PERIODICALIBM Journal Vol. 6 No. 3

TiTLE OF ARTICLE
Impulse Type . . . etc.

Impulse Voltage Circuit For U M With Recurrent Surge Oscillators.
I n p u t . . . etc.
On another page of the index the entry would appear as follows:38

IBM Journal Vol. 6 No. 3

Centigram Measu . . . etc.
Circuit For Use With Recurrent Surge Oscillators. Impulse Voltage
Circuit... etc
ge of PILOT:

IBM Journal Vol. 6 No. 3

Oscillators. Impulse Voltage Circuit for Use With Recurrent Surge
Oscillograph M a g a z . . . etc.
Oscillograph . . . etc.

Similarly, the other words of the same title, as well as the Journal title,
will appear indexed, and sorted in the left hand (index) position.
The Periodicals' dates will be keyed to each PILOT issue

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Figure 1. Brochure for Proposed Permuted Title Index Service
9;operations is n liable to continuous error 1 1 , — while Baxendale takes a middle ground:"Thus far the role of the computer i s chiefly that of research instrument; whether or not
it can fully assume the task of indexing is still in doubt11. - /1. 2 Scope of This Study
In view of the continuing controversy over the feasibility and evaluation of automatic
indexing techniques, a state-of-the-art survey and report is perhaps premature at thistime. The topic i s controversial on at least five grounds: First is the question, fMCjan
indexing be done by machine at a l l ? " Next,"Is what can be done by machine properly
termed 'abstracting*, 'indexing 1 , or 'classifying 1 ? n The.third moot point is "Is whatevercan be done by machine good enough, acceptable, as good as, or better than the productof human operations?" The fourth and most critical question is "How can we evaluate
acceptability or comparability for any indexing process whatsoever, whether carried out
by man or by machine or by machine-aided manuaj operations?" Finally, "If an indexing
product is to be achieved by machine, can it be done by statistical means alone, or must
syntactic, semantic and pragmatic considerations be brought to bear in the machine
decision-making p r o c e s s e s ? "The heat of controversy over any of these five grounds of debate is almost inversely
related to the availability of objectively validated evidence to which appeal might be made.
Thus, the literature on the topic to date i s typically colored by personal reactions bothpro and con, and even the cynics rely more on subjective judgments and personal preferences than on any substantial body of data. O'Connor cites typical claims of both proponents and opponents of the feasibility of automatic indexing, and he comments on both,"I have seen no good evidence offered in support of such a conclusion. "An impartial middle ground is offered by recognition that "To define a processordinarily thought to require human intellectual effort in such a way that it can be performed by a machine imposes a .rigor and a discipline on the definition which itself is invaluable to understanding the nature of the process i r .Z' Learning more about the indexing
process itself, through experimentation with machines, will provide "results of generalinterest, not just to those optimistic about machine indexing experiments 11 . $J In thissense, a state-of-the-art study is not premature. In this sense, therefore, we shall
explore the five questions listed above in subsequent sections of this report.

u
Farradane, 1961, [193], p. 236.
Baxendale, 1962 [ 4 2 ] , p. 69.

U
O'Connor, 1961 [447], pp 274 and 275.

±1
Swanson, 1962 [583], p. 288.

yBohnert, 1962 [ 6 9 ] , p. 9.

10

More particularly, in this survey of automatic indexing efforts, we will be concernedwith the following principal topics:(1)

A brief indication of the variety of ways in which punched card machines andcomputers can be and have been used in the preparation or compilation ofindexes. ±J(2) A more detailed consideration of the possibilities for machine generation ofindexes, specifically including:(a) Automatic derivative indexing, as in various examples of machine
extraction of keywords, where selection is based upon pre-specified
criteria, ^(b) Automatic assignment indexing, whereby the machine is programmed todetermine, in accordance with various specified criteria, whether or
not some one or more members of an established list of 'labels 1 (suchas subject headings, class names, descriptors, or other indexing terms)
should appropriately be assigned to the document or item in question, and(c)

Automatic classification techniques, on which such assignment-indexing
operations may or may not be based.
•

*

•

(3)

Consideration of the use of machines as relatively sophisticated aids to human
intellectual operations applied in either subject-content analyses or searchstrategy determinations.

(4)

Discussion of the question of evaluation of any index whatever, whether
manually or mechanically prepared.

(5)

Consideration of the implications of related research and development efforts,
specifically including:(a)Comparative evaluation of indexing systems,(b)Development and use of new types of "indexing" aids (in the sense of"pointing to11 and "indicative of11 the probable subject-content relevance)
to either selective dissemination or retrospective search of the technicalliterature,(c)Linguistic and logical -inference approaches to the elucidation of 'meaning'in natural-language m e s s a g e s , and(d)Theoretical approaches to the problems of determining ' 'member ship -in classes".

yNote that card-controlled camera systems, such as the Listomatic, and Addressograph machines have also been used for index compilations. See, for example, Shaw,
1951 [ 542], p. 49, who cites early use of the Addressograph for bibliographical work
by A. Predeek, "Die Adrema-Mas chine als Organizations mitt el im Bibliotheksbetriebe", Berlin, 1930, and E. Morel, "Les Machines au secours de la Bibliographie", Revue du Livre 1:14-19 (1933).Use of such devices is not included in thisreport, however, since they cannot be adapted to machine generation of indexes.
11(6) Appraisal of the current prospects for further research and development.
Certain difficulties of organization are evident. Thus many proposals precede actual
tests of techniques to which they are akin. Other proposals have been engendered as byproducts of or incidental to investigations of other techniques, such as those of text proc e s s i n g s derive by machine selected sentences which together may serve as automatically generated f 'abstracts 11 , more properly extracts. A/
This related subject of automatic abstracting, i. e . , the application of machineusable rules to the extraction or generation of textual information representing in condensed form that carried in the document as a whole, will not be of primary concern.
However, it will be noted that most of the automatic abstracting techniques so far proposed are potentially usable as tools for automatic indexing, especially in the trivial
sense that the automatic selection of index terms could be based solely upon the substantive words found in the machine-prepared extract. —' Further, since we are presumingthat a state-of-the-art review of automatic indexing techniques i s in some sense appropriate at this time, we shall emphasize the actual results of machine compilation andmachine generation of indexes and those investigations of assignment-indexing techniques
for which experimental or comparative data have been reported, rather than theoretical
approaches.

ySee, for example, Luhn, 1959 [ 3 8 4 ] , p. 4: "The principle of abstracting information by extracting certain portions or elements from the full text of adocument is particularly suitable to mechanization 11 ; Becker, I960 [ 4 4 ] , p. 13:"Perhaps 'extracting 1 would have been a better word than 'abstracting' 11 ; Edmundson
and Wyllys, 1961, [181], p. 227: "All proposed methods for making an automatic
abstract of a document involve using the author's own words by selecting complete
sentences, thereby reducing abstraction to the simple task of extraction. "I!
See Wyllys, 1963 [653 \ p. 22:"Automatic indexing is an area that seems
to us to be especially close to automatic abstracting, since the words and word
groups found to be most representative of a document for automatic abstracting
purposes are obvious candidates for entries in an automatic index for the
documents." See also Tanimoto, 1961 [594 ] , p. 235: "Thus after e x tracting k sentences which are a predetermined small fraction of the document,
we have an 'abstract'. To find the indexes to the document we take these ksentences and the corresponding sets of the canonical elements and consider
terms versus sentences instead of sentences versus t e r m s . • • The same analysis
i s then applied to this 'transposed' problem to produce the index terms"; Yakushin,
1963 [ 654], p. 17: "If some method can be employed for the automatic compilation of
abstracts, it can as well be used for the subject index. "12

1. 3 Derivative v s . Assignment Indexing
At least part of the provocation and controversy with respect to the possibilities forthe use of machines in indexing is due to confusion as to what type of indexing i s meant.
This in turn relates to a much older and broader controversy--that between fl word fl or
f,catchword n indexing on the one hand and "subject indexing 11 , "concept indexing 11 , or"controlled indexing" on the other.
In terms of operational definition, the contrast is best expressed in Luhn's distinction between index entries that are derived from the text of an item itself and thosethat are assigned to it from a list or schedule of subject categories, descriptors and thelike, which exists independently of the text of the item (Luhn, 1962 [ 372] ). 2 / In general,the differentiations that are made for the broader controversy, and the claims andcounter-claims made by the enthusiasts of either school, provide background for the
distinctions that should be made between various automatic derivative indexing operations
and whatever possibilities may be demonstrated for assignment indexing by machine.
In his text on information storage and retrieval Kent (1962 [315] ) contrasts word indexing as used in permuted keyword indexes, concordances and "pure" Uniterm systems with
controlled indexing which "implies a careful selection of terminology used in indexes inorder to avoid, as far as possible, the scattering of related subjects under different
headings. " He notes elsewhere that word indexing requires little subject-matter training
on the part of the indexer and little skill in indexing as such, and adds: "It is this type ofindexing that a machine can perform well.1—'
Like Kent, Bernier thinks that true subject or assignment indexing requires highly
trained human indexers. He says further:"The difference between subject and word indexing has been unclear at times.
Both types employ words, but only true subject indexing employs them withdiscrimination. Word indexing leads to omission of entries, scattering of related information, and a flood of unnecessary entries. Word indexing u s e swords as they are found in the material indexed with a minimum regard forstandardized meaning. . . i. 3 /Herner provides a further amplification of differences that are pertinent to consideration of indexing by machine, as follows: Z'ySee also Herner, 1962 [ 2 6 6 ] , p. 5; Skagg s a n d Spangle r, 1963, [ 5 5 7 ] , p. 60; Slamecka,
1963 [ 5 5 8 ] , p. 224. Mooers makes a similar distinction between "index terms which
are words or phrases extracted from the text and stylized conceptual t e r m s - - c l i c h e s- -which are assigned to the text">1963 [ 4 2 3 ] , p. 4.
Kent, 1962 [314], p. 268.
Bernier, 1956 [ 5 4 ] , p. 23.

±1
Herner, 1963 [267], p. 183.

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"The differentiation that is made between the two types of indexing is that word
indexing is inextricably tied to the words in a text: If a word appears it getsindexed as such; if it does not appear it does not get indexed. Concept indexing, on the other hand, has an element of abstraction in it: Words may either
be indexed as such or may be converted, either by themselves or in combination
with other words, into concepts which may not bear a.direct resemblance tothe words or combinations of words that evoked them in the indexe^s mind. "Machine techniques such as those of Luhn's KWIC, like the early Uniterm systems,
look no farther than the words used by the one author himself. Techniques such as thoseof Maron, Swanson, Borko, Meadow and Williams, among others, look specifically torelationships between words as used by one author to patterns of word usages in a given
subject area or given document collection. They may also look to these patterns as inturn related to prior human analytic judgments of the "ab outness" referrents of items in
the collection. In this sense, they at least attempt replication by machine of assignment
indexing.
There is no real question but that machines can in fact derive words from text provided that it is in machine-readable form. This machine procedure may involve direct
extraction of all words as index entries, as in a complete concordance. It may involvethe extraction of only those words which survive a "purging11 operation in which articles,
conjunctions, adjectives, and other "common11 words are first deleted. Various machinecontrolled modifications to such "derivative" indexing are also available. The case formachine achievement of assignment indexing for any but limited special cases is not soclear.
2.

INDEXES COMPILED BY MACHINE

A first and obvious use of machines in indexing processes is in the manipulation ofindex entries, previously selected on the basis of human analysis, to produce various
orderings, duplications and listings of these entries. The power of machine techniquesto speed and economize the sorting, ordering and listing operations in the preparationor compilation of indexes was recognized quite early, both in the field of library scienceand in the consideration of potential areas of application by specialists in machine
potentialities.
In particular, two specialized types of index, at least in the broad sense, are suchthat their compilation would be almost prohibitive in terms of time and cost were it notfor the use of machines. These are, respectively, the case of the complete index, theindex to all words of a text in their various contexts, which i s a concordance, i / and thecase of the "citation index", which has been used in the field of law for many years but
has only quite recently been suggested for literature search purposes related toscientific and technical information.

U
See, for example, Doyle,1963 [ 1 6 2 ] , . . p. 11: "Without data-processing
machinery, concordances are prohibitively expensive to generate for most u s e s
except in those cases where it is well known that a given volume of text is going
to be used again and again, by large numbers of people over a long period oftime. As we know, clergymen have made use of manually prepared concordancesof the Bible since the 12th century".

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