Multiparty Symmetric Sum Types

TL;DR

This paper develops a new theory of symmetric sum types for multiparty session types, enabling the modeling of non-deterministic, agreement-based choices among multiple participants, with applications in healthcare workflows.

Contribution

It introduces symmetric sum types for multiparty session types, allowing for non-deterministic, collaborative decision-making in protocols, and provides an embedding into existing types with proven properties.

Findings

Preserves typability and semantic correctness

Enables automatic translation and type checking of clinical guidelines

Supports efficient implementation of healthcare workflow tools

Abstract

This paper introduces a new theory of multiparty session types based on symmetric sum types, by which we can type non-deterministic orchestration choice behaviours. While the original branching type in session types can represent a choice made by a single participant and accepted by others determining how the session proceeds, the symmetric sum type represents a choice made by agreement among all the participants of a session. Such behaviour can be found in many practical systems, including collaborative workflow in healthcare systems for clinical practice guidelines (CPGs). Processes using the symmetric sums can be embedded into the original branching types using conductor processes. We show that this type-driven embedding preserves typability, satisfies semantic soundness and completeness, and meets the encodability criteria adapted to the typed setting. The theory leads to an efficient implementation of a prototypical tool for CPGs which automatically translates the original CPG specifications from a representation called the Process Matrix to symmetric sum types, type checks programs and executes them.