An Abstract Machine for Concurrent Modular Systems: CHARM

CHARM (for concurrency and hiding in an abstract rewriting machine) is an abstract machine which allows one to model naturally the behavior of distributed systems consisting of a collection of processes-sharing variables. CHARM is equipped with a clean operational semantics based on term rewriting over a suitable algebra, and it exhibits a sophisticated treatment of concurrency and modularity, which is obtained through the partition of each state into a global and a local part. To show the expressiveness and generality of this abstract machine, three relevant computational formalisms are mapped onto the CHARM framework: graph grammars, concurrent constraint programming, and place/transition Petri nets.