This is a 3-digit classification system (called the "Broad Area" internally by JPO)
that is oriented towards applications. ISTA has a list to the 2-digit level at the
URL
http://www.netaxs.com/~aengel/psttsmpl.htm#Broad area(s)
> In the STN guide for Japio, they mentioned that Japanese Patent
> Classification was in use for publications only before 1979.
There was an older Japanese Patent Classification system. The one in the online JAPIO
file is the still used Broad Area classification.