Session types have been introduced to provide global static descriptions of multi-process systems by specifying abstractions of the interaction patterns among a fixed set of participants. Deniélou and Yoshida’s paper extends this approach to dynamic multi-role session types that deal with time-varying, dynamic sets of interacting processes, thanks to the notion of roles. Introducing such flexibility is key to enabling the use of session types for dynamic interaction patterns such as the ones found in peer-to-peer (P2P) and client-server architectures.

A role denotes a class of process behaviors; it is characterized by a name, such as “broker” or “client,” which appears within a global multi-party session type that specifies the overall interaction pattern of a system. This global type can be restricted to a particular local type, which is the result of selecting in the global type the elements specific to a particular role name. These roles are key to the dynamic extension of session types. The authors suggest using universal quantification over roles to refer to the varying set of participants that implement a particular role, both at the type and implementation levels. Formal static and dynamic semantics rules, correctness theorems, and a specific-locking mechanism are successively introduced to firmly set the foundations of this approach.

Despite the importance of its possible future applicability, this highly abstract and notation-heavy paper will only be of use to computer scientists well versed in the intricacies of current programming language design formalisms.