  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.
