A study of atomicity and consistency in MMS servers

Abstract

Manufacturing message specification (MMS) is an application-layer protocol designed for the remote control and monitoring of industrial devices. MMS defines services for the manipulation of objects such as variables, domains, programs stored in MMS servers. Consistency is essential to the correct operation of these servers, in particular when the process controlled by the servers can lead to accidents or catastrophes. Concurrent access to shared objects, failures of the servers or cancellation of requests are examples of causes that can compromise the consistency of the set of objects in an MMS server. Atomicity and isolation, as components of the transaction paradigm, can help to support consistency of a set of objects. The purpose of this paper is to study atomicity of MMS services for two classes of objects: variables and domains. This study considers consistency at the server level only and shows that the designers of MMS were aware of the consistency problem but that no systematic approach was defined to prevent inconsistencies. The authors point out several places in the MMS standard where misconceptions or gaps appear in the specification of atomic services.