1Intnoducitxan

andb a c k g r o u n d

1.1 The project proposal
The research proposal BImproving access in an online publicaccess catalogue by automatic word stemming, spellingcorrection and limited synonym generation" was approved by
the British Library Research and Development Department
CBLRDDD and funded under grant 5I/G/720.
It proposed to investigate the following recall-improvement
devices:
automatic word stemmingsynonym and cross reference tables
5oundex-type keys for matching personal names
an n-gram technique for approximate matching of words
These were to be applied within a version of the Okapi
online catalogue developed under an earlier project.
These devices are not, of course, new. They all have along history, which is summarised in Chapters 3 - 5 .
5omeof our techniques are probably new, but the main emphasisin the design of the experimental systems was on ways ofapplying and presenting
the devices in an online catalogue
for general users.
1.2 Motivation
Rn online catalogue is a bibliographic reference retrieval
system. It differs from the "traditional" reference
retrieval systems such as Lockheed's DIOLOG in severalways :searches Bre done by untrained end-users rather than byor with the help of intermediaries
the subject coverage is often wide
the subject description in the records is inadequate oreven absent.

-1-1 Introduction

andbackground

In traditional information retrieval CIR3 intermediaries
use truncation and other "fuzzy matching". Inexperienced
and casual users will not generally do this, so a systemdesigned for such users should automatically carry out someof these procedures.
There are many cases where a search intermediary would
expand a searcher's query to include terms which cannot be
obtained by a simple application of grammatical rules
and/or recourse to lookup tables. The skills required to
do this involve the use of subject knowledge, linguisticknowledge and knowledge of the fileCsD being searched, andcannot be automated within the present capabilities of
linguistic computing.
However, the automatic inclusion of morphologically related
search terms and some tolerance of misspellings should bequite feasible with conventional hardware and software
techniques.
1.2.1

Feasibility

study

The likely utility of automatic query expansion had been
investigated by repeating subject searches from thetransaction Logs of the original Okapi system Csee 1.43.
More than a quarter of the searches would have benefitted
from a simple stemming procedure Cconflating singular andplural noun forms, "ing", "ed" and "s" verbal endings
etc.3. Occasionally, there would have been a decrease inprecision. Rbout a tenth of the searches contained apparently unnoticed spelling mistakes.
1.3 Staffing
The project head was Neil McLean, Head of Library Services
at the Polytechnic of Central London CPCL3. The proposerand director of the research was Stephen Walker. RichardJones was appointed as Research Officer in September 1985,and Nicola Johns as Research Officer/Programmer in June
1366.
1.4 Environment
The project aimed to build on the work of Mitev, Venner andWalker who designed and developed the experimental online
catalogue system, Okapi, under the BLRDD and Department ofTrade and Industry funded project "Microcomputer networking
in Libraries". The work of this project, proposed by Neil
McLean and Mel Collier, is reported in [13. Otherpublications include [2,3,4,5,6,73.
The original Okapi system will be referred to here as Okapi'84.
It is described in [13. Okapi '64 was an implementation of an online catalogue search system on a local area

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1 Introduction

andbackgroundtype index of personal surnames, which could lead to thedisplay of a selection of possible matches in the case of afailed personal name Look-up.
The intermediate system was never developed to the point
where it was robust and finished enough for public use
Calthough it stood up fairly well to the attention oflibrarians at BathD. Its specific item search willprobably be used for future public versions of Okapi, andthe subject search forms the basis of the systems describedin this report. The intermediate system is described in171.
The unfinished subject search facility of the intermediate
system included some of the features used in the systems
described in Chapters 6 and 7. The subject index consistedof words from titles, subtitles, subject headings and othersubject-rich fields of the MRRC record, and also Dewey
numbers. OIL words were subjected to the Porter algorithm,
and were combined using a combinatorial CRND/0R3 techniquewith inverse term frequency weighting as described in 6.5.
Records were output in decreasing weight order. There wasa small cross-reference list enabling terms to be treatedas synonymous: the list included CHILD and CHILDREN andsome other irregular plurals and alternative spellings.
Richard Jones carried out a substantial analysis of failed
searches, some of which was published in C8D. We constructed an inverted file of some 6000 subject searches
submitted to Qkapi '84 and used it to obtain a collectionof spelling mistakes and to suggest entries for an automatic cross-reference table CChapter 6 and Rppendix 53.
During the Summer and Rutumn of 1586 we designed and wrote
new subject search and indexing programs. Two versions of
the search program were produced. One - the •experimental"
system Creferred to as EXP1 - incorporates full two-Level
stemming, a substantial look-up table of phrases and equivalence classes of related terms and a spelling correction
procedure. The other program - the "control" or CTL system- has "weak" stemming but no look-up table and no spellingcorrection. It is unlikely that users would notice any
difference between the two programs unless a search carriedout on one was immediately repeated on the other.
There is also a third system, called 05TEM, which incorporates none of the recaLL-improvement devices. This was
only used for the repetition of users' searches by theexperimenters.

-4-1 Introduction

andbackground

In November Okapi '86 Csubject search only} was installedat two terminals in the Polytechnic's Riding House Streetlibrary.
The systems were alternated daily between the twoterminals. After a trial period, during which the system
was slightly improved, we began to collect data from Liveuse. Rbout 120 people were interviewed after they had
performed subject searches, and full transaction log data
was gathered from about 1100 searches Cabout 600 sessions}.
Rfter formal data collection had finished, the EXP system
was Left on site to collect further transaction log data.
Rt the time of writing we have collected Logs of some 7700
searches, and have done a certain amount of analysis of
this data where necessary to supplement the original set.
In parallel with the work outlined above, we were also
designing and developing programs for use in a second
project Con the use of relevance feedback in online
catalogues - 5I/G/7653.
While data analysis was being carried out, Nicky Johns
resigned. 5ince it would not have been possible to obtaina suitable replacement on what would have been a very shortcontract, we suspended work on the relevance feedback project so as to be able to complete the present project as
quickly as possible.
1.6 The report
Chapter 2 gives a brief survey of some of the probLems insubject searching in online catalogues. Chapters 3, 4 and5 survey ways of implementing the recalI-improvement
devices in IR systems in general as well as in catalogues.
The catalogues which we designed for this project aredescribed in Chapters 6 and 7. Chapter 6 describes themfrom the inside and Chapter 7 from the outside - how theuser sees them.
These two chapters are interdependent.
Their logical order may be 6 followed by 7, but their
psychological order may be the reverse.
Chapters 8 and 9 cover data collection, evaluation,and conclusions.

results

References
1 MITEV N N, VENNER 6 M and WRLKER 5. Designing an online
public access catalogue ; Okapi,a catalogue on a LocaL
area network(Library and Information Research Report393. London : the British Library, 1985.

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