We present a type theory for analyzing concurrent multiparty interactions as found in service-oriented computing. Our theory introduces a novel and flexible type structure, able to uniformly describe both the internal and the interface behavior of systems, referred respectively as choreographies and contracts in web-services terminology. The notion of conversation builds on the fundamental concept of session, but generalizes it along directions up to now unexplored; in particular, conversation types discipline interactions in conversations while accounting for dynamical join and leave of an unanticipated number of participants. We prove that well-typed systems never violate the prescribed conversation constraints. We also present techniques to ensure progress of systems involving several interleaved conversations, a previously open problem. 1

Abstract. We provide a formal model for expressing and analysing time-related properties of service-oriented systems. Our approach extends SRML, a high-level modelling language that we have been developing in the SENSORIA project. We introduce new primitives for SRML that capture several kinds of delays that can occur during service provision (e.g., the time taken by components to process events and perform computations, the time taken by the SOA middleware for discovering, selecting and binding services, etc.). Finally, we show how we can use the stochastic process algebra PEPA and its development environment to represent and analyse time properties of SRML models. 1