(1) the IPC is not expressive, i.e. the digital code hierarchy does not
necessarily reflect the conceptual hierarchy, and
(2) there is not necessarily a one-to-one correspondence between US and IPC
codes.
I should like to add one further cautionary note. It is important to realise
that IPC coding is not 'live' (by contrast with the ECLA codes in EDOC which are
updated monthly). This means that a comprehensive search should take account of
IPC codes that are currently applied (edition 6) as well as older ones (edition
5 and earlier), depending on the area of technology. In some of the chemical
areas I search, there was a flurry of activity in the IPC editions 4 and 5 so,
for any documents classified before 1985 or 1990 respectively, earlier IPC codes
need to be identified and searched. I usually identify these from the WIPO
IPCCLASS CD-Rom which contains all 6 editions or, alternatively, from the kind
of preliminary subject investigations described by several correspondents to
this list.
-- Julia M Fletcher, Quisitor Ltd 101567.2771@compuserve.com 60 Cherwell Drive, Marston, Oxford OX3 0LZ, UK Tel/fax: +44 (0)1865 728995