Knowledge Representations are ways of capturing knowledge and encoding it.  The foremost example is NaturalLanguage which has been with the human race in oral form for no-body knows how long and in written form for some more than 5000 years.  It achieved sophisticated form certainly no later than 500 BC or earlier -- the works of the great Greek philosophers ThreeOldGreeks dates from about the mid-350's BC --- today's versions include AI KRL's (Knowledge Representation Languages) ontologies and more commonly the various data base systems.

We still seem to have a long way to go though before we have a system that is complete -- See IncompleteNotations  --RaySchneider