LINGUISTICS AND INFORMATION SCIENCE:A POSTSCRIPT
Karen Sparck Jones
Cambridge University
andMartin Kay
XEROX Palo Alto Research Center
The object of Linguistics and Information Science (Sparck Jones and Kay, 1973) was toshow how far the suppposedly natural connection between linguistics and information
science existed in practice. We surveyed linguistic theory and computational linguistics toidentify approaches potentially applicable to information science, and to information, i.e.,
document, retrieval in particular; and we investigated the linguistic operations of automatic
document retrieval to establish their linguistic sophistication and the extent to which
linguistic theories were being, or could be, applied. We also looked for evidence of
feedback from automatic information retrieval to linguistics. Our general conclusion wasthat there was very little actual connection between linguistics and information retrieval.
Linguists were preoccupied by concerns rather remote from any practical activity like
information retrieval, for example the properties of linguistic theories, and had failed toprovide tools of potential utility to retrieval workers. At the same time, in both practiceand research in information retrieval, needs which might be met by linguistic theory were
not properly specifi-d. In general, the linguistic procedures of automatic information
retrieval were found to be very simple, and it was not obvious how useful refined linguistic
tools would be, either as aids to automation, or as devices for improving retrieval
performance.
In this note, we shall briefly consider the major developments in linguistics andinformation retrieval that have taken place since we completed the manuscript of our bookin mid 1971, to see whether linguistics and information science are, or could be, moreclosely linked now than they were then. The note is not intended to be a detailed survey,
but rather a set of comments within the general framework of Linguistics and Information
Science. Our remarks are therefore independent of the other papers in this volume, andthe reader is referred to these papers for more detailed treatments of individual topics,
from different points of view.
Linguistics
Theoretical Linguistics. In 1971, transformational grammar, in one version or another,was clearly the dominant linguistic theory in North America and was gaining adherents
throughout the world at a rapid rate. Even in countries like England, Denmark, and183

Karen Sparck Jones and M a r t i n Kay
Czechoslovakia, with vigorous linguistic traditions of their own, it appealed to many as theparadigm most likely to shed light on outstanding linguistic problems. However, already by
the time our book was published, the term transformational grammar could no longer beused to refer to a single coherent body of doctrine. In Aspects of the Theory of Syntax,
Chomsky, (1965), proposed the theory according to which sentences had underlying
structures generated by a context-free base component. The sentences themselves wereobtained f r o m these by the application of transformational rules which did not, however,
have any effect on meaning. Optional tranformations made it possible to derive sets o f
two or more sentences f r o m the same underlying structure, but, in these cases, it wasclaimed that all the sentences in the set would have the same semantic interpretation. It
was an appealingly simple view and constituted a strong claim about the nature of humanlanguage. But i t proved impossible to uphold this claim. It soon appeared that certain
aspects of semantic interpretation, notably those concerning the use of quantifiers,
depended in crucial ways on the surface forms of sentences. So, f o r example, "Everycommand is represented by a single code" is to be interpreted quite differently f r o m " A
single code represents every command".
"He sent his daughter her allowance" has adifferent range of meanings f r o m "He sent her allowance to his daughter".
Attempts to adjust the theory to account f o r facts such as these took a great variety o fforms. The proponents of generative semantics pursued the view that deep structures
should be more "abstract", that is, more remote f r o m the sentences they underlie and that amore complex transformational apparatus should relate them to surface forms. According
to this view, no separate semantic component is required because the deep structure is thesemantic interpretation. This was typically combined with the proposal that the theory
specify a set of transderivalional
constraints restricting the sequences of transformationalrules that could apply to a given deep structure. The introduction of such heavy machinery
could be justified, in the face o f the requirement for explanatory adequacy, only i f thesecontraints were part of the overall linguistic theory and not a separate part of the grammarof each language.
Another view was that the requirement that transformations should play no semantic role,and that the meaning of a sentence should be derivable entirely f r o m its deep structure,should be weakened or abandoned. Jackendoff (1972), f o r example, proposed a scheme
according to which the meaning of a sentence would be derived f r o m a number of its
representations, including the deep and surface structures, and also other structures thatarise in the course of the transformational process.
However, it rapidly became clear that there was a great deal more than quantifiers andrelated logical problems to embarrass the theoreticians.
They became increasingly
impressed by the fact, never doubted by their colleagues in Europe, that the notion o fsemantic equivalence cannot be identified with that of logical equivalence. American
linguists becane increasingly interested in what has been called functionalism, broadly, theways in which various kinds of utterance suit themselves to achieving the various goals thata speaker might have. This was stimulated, in part, by the notion of speech acts put
forward by Austin (1965) and Searle (1969). It is observed that the difference between thesentence "I will be in the office tomorrow at noon" and "I promise to be in the o f f i c etomorrrow at noon" comes not f r o m any difference in the truth values of the propositions
they represent, but f r o m the nature of the commitment in which they engage me, thespeaker. Predictably, the response of the generative semanticists was to decorate the alreadyovergrown trees they proposed as the deep represertations o f sentences with a new layer o f
structure to accomodate performative verbs. "John ran" came to have a structure more likethe one that would previously have been ascribed to "I assert that John ran", in which theperformative "assert' declares the kind of commitment that the speaker has to what

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follows.
A related notion is that of presupposition. The sentence " I like your new car" is true i f I
like it and false i f 1 do not. But what i f you do not have a new car? In this case, neither
the sentence "1 like your new car", nor its negation " I do not like your new car" is true. The
purely contingent fact that you do net have a new car cannot render the sentence
meaningless. The trouble is that both sentences imply that you have a new car and, because
this implication is false, the phrase, "your new car" fails to refer properly. If a sentence
and its negation both imply some proposition, they are said to presuppose that proposition.
The notion of presupposition impacts the interpretation of natural sentences in various andoften subtle ways. The sentence "Brutus killed Caesar" and " I t was Brutus that killed
Caesar" have the same truth value—each is true i f and only i f the other i s - - b u t the second
presupposes that someone killed Caesar whereas the first does n o t
Speech acts and presupposition belong to a class o f essentially pragmatic phenomena whose
study cannot be confined to the limits o f single sentences. They are phenomena thatcannot be summarily excluded f r o m the study of linguistics for, just as it proved impossible
to conduct a deep investigation o f syntax without regard to semantics, so now it proves
impossible to investigate semantics satisfactorily without regard to pragmatics. As a result,linguists f i n d themselves committed to a view of language in which the status of individual
sentences is greatly reduced.
These problems are still very poorly understood and certainly no theory with the formal
elegance of transformational grammar has been proposed to accommodate them.
Apessimistic appraisal o f the resulting situation is that American linguistics is in a state o fcomplete disarray with no common body of doctrine to unite even small groups oftheoreticians.
As viewed f r o m London or Prague, the situation might appear moreencouraging i f only because, f r o m these vantage points, transformational linguists have atleast demonstrated the maturity to face what are, after all, quite old problems. On theother hand, the considerably longer time that Halliday, Firbas, Sgall, and their European
colleagues have spent with these problems has provided little in the way of solutions.
Computational
Linguistics.
Sparck Jones and Kay (1973), adopts the characterization ofcomputational linguistics, due to Hays, (1967), as "those linguistic activities in which thecomputer plays a central role". A better characterization, especially in view of more recent
work, might be as linguistics in which computation provides a major source of inspiration.
The breakdown of the transformational paradigm and the need which many more linguists
now feel to examine linguistic phenomena in a wider context have done much toundermine the distinction between competence and performance. Consequently, there isrenewed interest in studying the strategies that people employ in producing andunderstanding utterances as well as abstract constraints on the forms they can take. It is
not surprising that this line o f attack has never been pursued far in the past because thevocabulary and metaphors necessary to investigate complex abstract processes were simply
not available until they were provided by computer science. The term "computational
linguistics" can therefore be properly applied to linguistic activities that do not involve
actual machines at all. To the extent that they make use of notions of variable binding,control structure, process scheduling, and the like, they are computational.
Starting f r o m an original idea of Thorne, Bratley and Dewar (1968), further developed by
Bobrow and Fraser (1969), Woods (1970), developed a parsing scheme based on what hecalls an Augmented Transition Network Grammar ( A T N ) (see also Sparck Jones and Kay,
1973, pp. 100-101). This parser was incorporated into at least two question-answering
programs, one f o r the U.S. Defense Documentation Center and the other, f o r use on

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geological information collected on the moon, for NASA (Woods et al., 1972). Thesesystems attracted much attention because of the unprecedentedly wide coverage of theirdictionaries and grammars and also because of the overall smoothness and efficiency withwhich they worked. The English grammar that these systems incorporated was written
largely by Kaplan who also wrote the grammar of the MIND system (see Kay, 1967). Basedon similarities that he perceived in these apparently very different systems, Kaplan (1973),
designed what he called the General Syntactic Processor which generalizes and greatly
simplifies the two preceding techniques. Furthermore, it makes a clear distinction between
the grammatical rules approximately modeling a speaker or hearer's competance and a setof scheduling rules which, by determining which of the possible courses of action open to
the processor at any given moment will be followed, enshrine the processing strategies.
At the same time, a new syntactic formalism, called relational grammar was being
developed by Postal and Perlmutter (forthcoming) which Lakoff and Thompson (1975),
saw as having a strong family resemblance with the grammars of Woods and Kaplan. It
thus appears that what began as an engineering device to meet very practical goals has,through a series of successive refinements, become a theoretical contribution to linguistics.
The interest of this particular contribution is that it provides a basis upon which to makepredictions about details of human linguistic behaviour which are susceptible ofexperimental verification (see Kaplan, 1972).
At the beginning of the period covered by this postscript, Winograd (1972), completed his
SHRDLU system, a computer program v/hich manipulates children's building blocks (asdepicted on a two-dimensional display) in response to directions given to it in English. Theinterest of the program lies mainly in its ability to make simple but natural inferences
about what it is told to do. If it is told to put the red block on the green one, but the green
one has a yellow one on top of it already, then it infers that it must remove this first
Sometimes it must make quite complex preparations before the final result it has been
directed to achieve can be reached. Asked why it made this or that move, it will respondwith an acceptable explanation. Thus, if one asks "Why did you move the yellow block?" itwill say something like, "Because I wanted to put the red block there." The system will
respond correctly to commands to build relatively complex structures, like towers, out of
the blocks and will accept definitions of hitherto unknown words denoting new structures
to be built
Also during this period, a very considerable amount of money has been spent by the
Advanced Projects Research Agency of the US Department of Defense on research directed
towards speech understanding (Newell et aU 1973). Speech understanding is to be clearly
distinguished from speech recognition in that it aims to go beyond the recognition ofisolated spoken words and to respond in some potentially useful way to connected speech.
This work, conducted at a number of centres in the United States, led to a considerablyincreased understanding of how phonetic and phonological data might be processed andhow this might be integrated with work on semantics and syntax already under way. In
particular, it led to the development of more flexible methods of managing the interaction
between the various components of a large computer system. Very early in this work, it
became clear that the established view that a linguistic processor could consist of a series ofcomponents, each taking as input the output of the one before, was no longer viable.
Recognition of phonetic units in the acoustic signal required not only the data in thatsignal, but also predictions about what later parts of the signal might contain based on asyntactic and semantic analysis of what had already been heard. It was necessary to devise
schemes whereby the components could work essentially in parallel, each being prepared toaccept and deliver partial results, hypotheses, and predictions, even at a very early stage in
the analysis.

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Linguistics and Information Science: A Postscript
The systems we have been discussing had the common property that they could process
successfully only carefully constructed sentences about the very narrow subject matter forwhich they were designed. They were designed arounc what has come to be known as a
microworld. The extent of their contribution to linguistics, computational or general, istherefore very much an open question. Such attempts as there have been to apply themethods of linguistics to larger universes of discourse or to larger subsets of the language
have rested on much more modest goals in linguistic analysis. The extreme position isrepresented by a program called PARRY (Colby 1973) which plays the part of a paranoid
patient in a dialog with a person who is expected to play the role of a psychiatrist. In this,as in much other psychiatry, the object is not to cure the patient, but to prolong the dialog.
The program is accounted successful to the extent that it sustains the illusion of a dialog
with a real patient. What is interesting about the program is that it. rests on none of theadvanced theories and complex techniques that are the basis of the other programs we havediscussed. Yet it is the only one that will perform successfully in the hands of a naive anduntrained user. This success is, of course, largely attributable to the carefully chosen
scenario within which the program operates. The well-formedness conditions on aconversation between a psychiatrist and a sufficiently sick parent are presumably minimal.
It is however interesting that the illusion of continuity can be maintained at all, and it atleast suggests that a considerable amount may yet be achieved by relatively simple
techniques provided only that they take into account whole texts or whole discourses rather
than single sentences.
But, while recognizing the limitations of the approaches described, it can be said that there
has been progress in computational linguistics since 1971; in particular, the systems
implemented, though small, have been quite solid. Computational linguistics thus appearsof more potential relevance to information retrieval than it did then.
Information

Retrieval

In information retrieval, the most striking development since 1971 has been the growth ofon-line search systems for very large data bases. The automation of library operations ingeneral has continued, in both small and large libraries, a notable development being the
growth of library networks, for example involving communal cataloguing, as in the Ohio
College Library Center. But the development of on-line search systems is more interestingin the present context, since it depends on linguistically interesting procedures of indexing
and searching. It is therefore all the more disappointing, from our point of view, thatthese systems do not generally involve sophisticated automatic linguistic operations. Their
effectiveness derives in large part from their computational power, since they can scan
extremely large files for items satisfying complicated specifications, in a mariner which isquite impossible for the human library user. As Lancaster and Fayen's 1973 survey shows,these systems may offer a whole range of search keys, and depend on a variety of linguistic
indexing modes, including on the one hand manual indexing using a controlled thesaurus,
as in Medline, and on the other the exremely simple form of automatic indexing
represented by the provision of unprocessed title and abstract texts.
Since these systems to a considerable extent simply provide mechanical support for thehuman searcher, rather than an automatic substitute for him, indexing can be seen as
request rather than document oriented. This is particularly obvious when title or abstracttexts are searched. Linguistic entities like word classes or phrases are generated forindividual requests, and corresponding very fine partitions of the document set are
established on searching rather than when documents are filed. While any request above
the single word incorporates an element of a posteriori indexing, current automatic searchsystems may permit extremely complex specifications, including, for instance, very variable

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truncation options, and so emphasize indexing as a request rather than a documentoriented process. At the same time, the fact that searching in on-line systems is interactivemeans that a whole range of information about words and documents is exploited, but notnecessarily in a systematic or coherent manner. These systems are hopefully hospitable to agreat variety of needs, and allow great flexibility in searching. They are, in consequence,extremely difficult to characterize in terms of language-using processes and to evaluate.
The variable human elements involved mean that it is not at all easy to establish therelative value of different types of linguistic information or different linguistic procedures.
Perhaps the only strictly innovative feature of these systems is the provision of statisticalinformation, e.g., about the collection frequency of index terms as a guide to theireffective, as opposed to notional, discriminating power. Some tentative steps have beentaken in the use of statistically based weighting schemes. Statistical information is,perhaps, of marginal linguistic interest, being essentially descriptive of the sublanguage
represented by a document collection, rather than systematic. But it is one of the few
distinctive contributions of the computer based approaches to indexing studied in thenineteen sixties. Statistical weighting is also an active research area. In the absence of
richer, automatically obtained information, getting some mileage out of such easily
obtained data is an attractive option, particularly since such experiments have been carriedout, for instance by Salton (Salton and Yang, 1973) and Sparck Jones (1972), suggest thatterm occurrence information can be sucessfully exploited to improve retrieval performance.
In A Theory of Indexing, Salton (1975), analyses the retrieval value of term frequencies ina systematic way, and argues that terms with frequencies in different ranges should be
handled in different ways to modify their matching behaviour. Thus, if medium term
frequencies are most useful for both recall and precision, low frequency terms may begrouped in classes to increase their effective frequency, and high frequency terms combined
as phrases to reduce theirs. Roberts and Sparck Jones (1976), have suggested that retrieval
performance may be further improved if weighting is based on information about relevant
document distribution of terms, and report successful experiments along these lines.
Statistical term classification, on the other hand, has not been proven effective, andresearch on this and other topics of interest in the nineteen, sixties seems to have declined.
Work continues on document clustering, including that based on linguistically eccentrickeys like citations. But, in general, the situation in information retrieval, and particularly
in research, is very different from that in 1970. On the other hand, technological advances,like the provision of on-line searching appear to have removed the need for autonomous
automatic document and request processing. Manual indexing and the use of manuallyconstructed thesauri have also been maintained, partly through organizational inertia,
partly because their cost can be spread over a great many information products, partly
through continued faith in their merits, and partly because sufficiently comprehensive andrigourous experiments demonstrating their ineffectiveness, or showing that less exigent
indexing techniques are superior, have not been carried out. An example of a continuingcommitment to manual indexing, not merely because automatic substitutes have not yet
been provided but because the human indexer is believed to be necessarily superior to acomputer, is the British Library's PRECIS system (Austin, in this volume). It has also beenrecognized that retrieval system use and performance are affected, or determined, by otherfactors than the core linguistic ones of primary concern in the nineteen sixties.
Irrespective of whether specific linguistic information can be obtained automatically as
opposed to manually, its utility may be small. Librarians have doubtless known this allalong, but in automatic retrieval systems, 'sociological* factors have only recently been
given their due.
On the other hand, it must be accepted that retrieval research has not altogether produced

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the goods.
Sparck Jones 1974 survey in Automatic
Indexing
1974 showed thatcomparatively few reasonably scaled and rigorous experiments have been carried out which
individually and collectively provide comprehensive and systematic data on the relative
merits of automatic and manual indexing, or linguistically complex and linguisticallysimple indexing. It is even true that adequate tests of complex and simple manual indexing
are lacking. However, research workers can defend themselves by pointing to a manifest
reluctance on the part of system operators to consider research problems or take muchnotice of apparently relevant results; and by noting the change in experimental
requirements accompanying operational system growth. In the nineteen sixties, experiments
on a few hundred documents might be deemed operationally relevant. They would not be
acceptable now, and, while it is evident that larger tests are needed because scale effects inretrieval are not well understood, this makes retrieval research more expensive and time
consuming. The design of experiments relevant to o n - l i n e searching also presents many
problems, and it is not at all obvious how sociological factors in retrieval systems should bestudied, and their significance determined.
Referring to the more detailed topics of Linguistics
and Information
Science, specificremarks about the linguistic elements in retrieval systems can be made as follows.
Automatic syntactic analysis for indexing is currently virtually non-existent. Work on thef u l l syntactic processing of particular kinds of data f o r particular purposes is being
undertaken by, for instance, Sager (in this volume) which, if successful, might have somebearing on document indexing in general. Partial parsing to identify words or word strings
as candidate indexing terms is being applied on a large scale by Klingbiel (1973a,b), and at
the lowest level m i n i m a l syntactic i n f o r m a t i o n may be exploited f o r the production o fprinted indexes. Syntactic i n f o r m a t i o n may also be tacitly exploited via request
formulations involving combinations of words in a specified order or in specified
proximity. But, f o r a linguistic point of view, such work is small beer. The question as tohow far syntactic information can be of general u t i l i t y in document retrieval indeed
remains unanswered, though f o r printed subject indexes, f o r example, it appears of value.
Work on automatic syntactic analysis f o r i n f o r m a t i o n retrieval must thus depend on
further analysis of the kind of syntactic information that is really needed f o r retrieval, andhow it should be exploited.
Under the semantic head, the n o n - t r i v i a l selection o f words f r o m longer texts is rarely
undertaken, all the n o n - f u n c t i o n words of titles or abstracts being taken as index keys orleads to keys. (Specialized applications like legal or patent text searching are exceptions.)
Automatic vocabulary formation and control has, in recent years, been approached chiefly
through weighting, as described above. Clearly, some selection is achieved i f terms are
zero-weighted, and, more generally, control is achieved through the different values
determined by weighting.
It must be emphasized that vocabularies characterized byweighting techniques are sensitive to changes in the composition of a document collectionin the way that a priori vocabularies are not; a term may be a good discriminator at one
stage in the life of a collection, but a bad one at another. The automatic identification ofterm relations is not being very actively pursued. As with syntax, the apparent failure o fplausible approaches to the automatic identification and use of semantic relations haveincidentally cast doubt on the retrieval value of such relations, however identified. As
noted, many manual thesauri continue to be used, but the real and relative values o f thetypes o f i n f o r m a t i o n they may contain have not been determined in detail, and experiments
to obtain such i n f o r m a t i o n automatically therefore seem rather pointless.

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Karen Sparck Jones and Martin Kay
Conclusion
In conclusion, can we say that the relation of linguistics and information retrieval in 1976
differs from that of 1971? The foregoing does not show that there is greater actual
connection between the two now than there was then. However, the relative positions havechanged.
Linguistics, particularly computational linguistics, seems more potentiallyapplicable to information retrieval than linguistics did in 1971. On the other hand, in
information retrieval there appears to have been a retreat from linguistic sophistication,and there is hence less interest in automatic language processing techniques of the kindcurrently being studied by computational linguists.
We nevertheless do not feel that linguistics and information retrieval can have noconnection, though we see the difficulty of making the connection more clearly than we
did in 1971. Essentially, the concerns of information retrieval and current linguistics areof a different scale. Information retrieval is necessarily concerned with the larger featuresof the masses of information represented by document collections, and with grosscharacterizations of individual documents. Linguistics is typically concerned with a refined
characterization of small universes and units of discourse. The techniques required toapproach linguistic information on these different levels seem to be very different. At thesame time, the scale distinction between the concerns of linguistics and information science
are not consistent over different aspects of language processing; for instance, linguists may
require a very large grammar :o provide a sufficiently precise characterization of individual
sentences, where information scientists might get by, for gross characterization, with asmall one. Thus, at virtually every linguistic point, there is some substantial difference inscale.
However, we persist in our optimism and foresee greater possibilities for collaboration in
the future. We take hean particularly from two facts: first, linguists are turning theirattention more and more to larger units of discourse than the sentence, and second, on-line
retrieval systems are likely to involve retrievable units smaller than traditional documents.
We believe that the relevance of these fields to one another will become more apparant as
the size of the text units they deal with becomes more commensurable.
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