I recommend looking at fusion calculi, which are based on the idea of input/output being symmetric. They were invented independently by B. Victor together with

I recommend looking at fusion calculi, which are based on the idea of input/output being symmetric. They were invented independently by B. Victor together with J. Parrow, and at the same time by Y. Fu. See [1] for some links. NB this is an old page, and I don't think anyone currently works on this. When it was first released, Microsoft's BizTalk was based on a generalisation of Fusions. (L. Wischik, the author of [1] what on the BizTalk team.) [1] http://www.wischik.com/lu/research/fusions.html http://www.wischik.com/lu/research/fusions.html