Lexikon-Sonate is a work-in-progress which was started in 1992. Instead of being a composition in which the structure is fixed by notation, it manifests itself as a computer program that composes the piece - or, more precisely: an excerpt of a virtually endless piano piece - in real time. Lexikon-Sonate lacks two characteristics of a traditional piano piece:
there is no pre-composed text to be interpreted, and
there is no need for a pianist or an interpreter.
Instead, the instructions for playing the piano - the indication "which key should be pressed how quickly and held down for how long" - are directly generated by a computer program and transmitted immediately to a player piano (or the built-in Quicktime synthesizer) which executes them.