KRL is a knowledge representation language, developed by Daniel G. Bobrow and Terry Winograd while at Xerox PARC and Stanford University, respectively. It is a frame-based language. KRL was an attempt to produce a language which was nice to read and write for the engineers who had to write programs in it, processed like human memory, so you could have realistic AI programs, had an underlying semantics which was firmly grounded like logic languages, all in one, all in one language.