STUDIES ON PATENT CITATION NETWORKS

DOIhttps://doi.org/10.1108/eb026650
Publication Date01 Jan 1978
Pages12-20
AuthorP. ELLIS,G. HEPBURN,C. OPPENHEIN
SubjectInformation & knowledge management,Library & information science
STUDIES ON PATENT CITATION NETWORKS*
P.
ELLIS
Kodak Limited, Harrow
G. HEPBURN and C. OPPENHEIN
Centre for Information Science, The City University
Work is described on patent citation networks, a novel technique for dis-
playing the history of technological subjects and their key turning
points.
The
method accurately identifies the key patents in a subject field, and if a subject
docs not have
a
definite starting point, this
is
reflected in the patent network.
The networks
are less
satisfactory if the key patent took
a
long time to appear
in print. Subjects studied were: semi-synthetic penicillins, tobacco substi-
tutes,
electrophotography, Ziegler-Natta catalysis, and hovercraft. Possible
uses of the technique are examined.
INTRODUCTION
THE STUDY of the history of science is a well-established academic discipline,
and a number of techniques for identifying major contributions to the develop-
ment of science have been devised. One of the most important of these is the
historiograph approach developed by Garfield.1-4 In this approach, a graphic
display of citation data that shows key scientific events in chronological order is
prepared by linking one paper to another that it cites with a straight line. Papers
that have been highly cited by other papers and therefore presumably of impor-
tance, can easily be identified by this graphic technique. The validity of the tech-
nique can be tested by constructing and then comparing two historiograph net-
work patterns for a given subject; one is prepared from a standard historical
account, and the other using citation relationships. Such a comparison, using
the discovery of the structure of DNA as the subject under study, has demon-
strated the validity of the technique.2 The historiograph method has been more
recently applied to the history of amorphous semiconductors,5 and of bridge
design.6 These are technological subjects, but journal articles only were con-
sidered.
Up until recently, no work has been carried out using these techniques on
patents, despite hints that such studies could prove valuable.6-9 This lack of study
of patent citations can be attributed to three main factors. Firstly, in sharp contrast
to journals, relatively few countries' national patent specifications publish cita-
tions.
Secondly, there is no convenient source of patent citation data analogous
to I.S.I.'s journal citation magnetic tape data. (At one time, Science Citation Index
included US patents as source documents10 but this practice was dropped many
years ago.) Thirdly, citations in patent specifications do not serve the same pur-
pose as citations in journal articles. Patent citations are made by the examiner to
warn the applicant of related work which affects the novelty of his invention.
* Part of this paper was presented to the International Symposium on Patent Information
and Documentation, Munich, May 1977.
Journal
of
Documentation,
Vol. 34, No. 1, March 1978, pp. 12-20.
12

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