Controllable-choice Message Sequence Graphs

TL;DR

This paper introduces controllable-choice Message Sequence Graphs, a restricted class ensuring realizability and deadlock-free execution, addressing the undecidable general case of MSG realizability.

Contribution

It defines a new subclass of MSG, controllable-choice MSG, that guarantees realizability and deadlock-freedom, and proves its maximality among known subclasses.

Findings

All models of controllable-choice MSG are realizable.

Decidability of membership in the controllable-choice class.

Largest known subclass of MSG with deadlock-free realization.

Abstract

We focus on the realizability problem of Message Sequence Graphs (MSG), i.e. the problem whether a given MSG specification is correctly distributable among parallel components communicating via messages. This fundamental problem of MSG is known to be undecidable. We introduce a well motivated restricted class of MSG, so called controllable-choice MSG, and show that all its models are realizable and moreover it is decidable whether a given MSG model is a member of this class. In more detail, this class of MSG specifications admits a deadlock-free realization by overloading existing messages with additional bounded control data. We also show that the presented class is the largest known subclass of MSG that allows for deadlock-free realization.