Global Types for Open Systems

Abstract

Global-type formalisms enable to describe the overall behaviour of distributed systems and at the same time to enforce safety properties for communications between system components. Our goal is that of amending a weakness of such formalisms: the difficulty in describing open systems, i.e. systems which can be connected and interact with other open systems. We parametrically extend, with the notion of interface role and interface connection, the syntax of global-type formalisms. Semantically, global types with interface roles denote open systems of communicating finite state machines connected by means of gateways obtained from compatible interfaces. We show that safety properties are preserved when open systems are connected that way. We prefer to use the word role rather then participant since interface role sounds more suitable for the present setting than interface participant.

Open Multiparty Sessions

“…Instead in the present paper we can use the standard syntax to build the global type of the session obtained by connecting. Moreover, we have shown that the compatibility relation of [1], which requires duality, can be relaxed to a relation strongly similar to session-types' subtyping [14,11]. Our structural preorder on processes mimics the subtyping relation between session types of [7], which is a restriction of the subtyping of [11].…”

“…In the present paper we have provided a multiparty formalism and we have adapted the approach of [1] to it. Our calculus of multiparty sessions is like those of [12,15], but for the use of coinduction instead of induction which is inspired by [6,27].…”

“…A relevant feature of our formalism is that the connection operation on systems can be "lifted" to the level of global types. In [1], where systems of CFSMs were taken into account, such a lifting was done by extending the syntax of global descriptions with a new symbol, whose semantics is indeed the connection-by-gateways at system level. Instead in the present paper we can use the standard syntax to build the global type of the session obtained by connecting.…”

“…In [1] a methodology has been proposed for the connection of open systems, consisting in replacing any two participants -if their behaviours are "compatible" -by two forwarders, dubbed gateways, enabling the systems to interact. The behaviour of any participant can be looked at as an interface since, without loss of generality, the notion of interface is interpreted not as the description of the interactions "offered" by a system but, dually, as those "required" by a possible environment (usually another system).…”

“…The main tool is a function from the global types of the original systems to the global type of the system obtained by connection. In the present setting it is also possible to investigate in a clean way the notion of interface compatibility: we show that the compatibility relation used in [1] can be relaxed to a relation closely connected to the observational preorder of [27], in turn corresponding to the subtyping relation for session types of [14,11].…”