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cards are placed in the alphabetical sequence in the alternative
places, referring to the keyword chosen.
3.6.2 There are practical difficulties associated with such systems,
like the time taken to compare numbers when the system is used
for a large collection of documents. The Central Building Research
Institute considered 20,000 documents as the maximum capacity
of their system. However, since comparing numbers is a simple
clerical operation, there is plenty of scope for the use of computers.
This approach to retrieval has been widely adopted in the USA and
may well be followed elsewhere. A cheaper solution to this problem
is the use of optical coincidence cards. In this system, holes are
punched in the cards to represent document numbers. The cards
for relevant terms are held together and light shines through the
holes only where there is a document in which the entire set of
terms is represented. In the UK, the Library of the Building
Research Station and the Overseas Geological Surveys both use
such a system for the organisation of their documents. The cards
used in connection with this system usually have a maximum
capacity of 10,000 holes. This is not, however, the maximum
capacity of the sytem as new sequences can be created with or
without a master key-file.
3.6.3 Punched cards have been used for the organisation of
information in some libraries and information centres. Where
edge-notched punched cards are used, the holes around the peri
meter of the card are used to represent subjectterms or bibliograph
ical information. Cards are retrieved by placing a needle or needles
through the appropriate hole or holes separating those cards which
have been notched in that position (these positions) from those
which have not. Superimposed coding can be used. Centre punched
cards have a much greater capacity, and there is a wide range of
equipment (sorters, tabulators, etc.) which extend their capabilities.
The holes in these cards can be divided into fields each representing
a facet of the subject, and the information retrieved by sorting over
the appropriate number of columns.
3.6.4 The Documentation Division of Athens Centre of Ekistics
use a computer to obtain rapid and effective control over literature.
A 90-column punched card is used as input12 columns are devoted
to the author's name and one initial, 48 to subject data, 17 to other
bibliographical data, and 7 to information included in the 'Ekistics
Grid'. The key to the whole system is the selection of four words to
express the subject content of the article. This must be done by
means of a logical English sentence that can be easily understood.
To make up this sentence, additional words may be used within
the limit of space available. These words appear in the printout
but are not to be permutated by the computer. A monthly subject
index is produced and reproduced by thermofax for distribution
to professional and technical staff at the Centre. A dictionary of
words used as keywords and synonyms that have been identified
