DoubleTalk was a music composition system developed 1984-6 by Stephen Pope, then at PCS/Cadmus Computers in Munich. It was based on a Petri Net design/simulation package called MoBY developed by students at the University of Dortmund under the direction of Georg Heeg.
The main DoubleTalk publications (both by S. T. Pope) are:
"Music Notation and the Representation of Musical Structure and Knowledge." in Perspectives of New Music 24(2), Winter, 1986, 34 p.
"The Development of an Intelligent Composer's Assistant: Interactive Graphics Tools and Knowledge
Representation for Composers." in Proceedings of the 1986 International Computer Music Conference,
The Hague, October, 1986, 16 p.
Many of the ideas of DoubleTalk have been carried through the author's more recent systems, including the HyperScore ToolKit, MODE, and now Siren -- see http://www.create.ucsb.edu/Siren/.