On the Impact of the Communication Model on Realisability

2025-12-05

AI Summary

Existing work on multiparty session types primarily assumes peer-to-peer semantics and lacks a unified theory for cross-model realizability—i.e., how communication models (e.g., packet-based, causally ordered, synchronous) affect protocol realizability, despite their critical role in distributed systems. Method: We propose a unifying analytical framework integrating type theory, global/local type projection, complementarity analysis, and complexity-theoretic characterization. Our approach supports verification across complexity classes from NLOGSPACE to EXPSPACE. Contribution/Results: We establish that communication models do not affect subtyping relations but critically determine realizability. We develop the first cross-model realizability theory and a sound, complete decision algorithm for realizability. Our results enable joint decidability of realizability and subtyping, precisely characterize computational complexity boundaries under varying communication assumptions, and provide both theoretical foundations and algorithmic support for deploying session types reliably in heterogeneous distributed systems.

Technology Category

• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories
• Knowledge Representation and Reasoning: Computational Complexity of Reasoning
• Multiagent Systems: Agent Communication

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Data transparency and provenance
• Graph Algorithms and Modeling for the Web: Algorithms and analysis for incomplete, noisy, or partially observed Web-related graphs

Abstract

Multiparty Session Types (MPST) provide a type-theoretic foundation for specifying and verifying communication protocols in distributed systems. MPST rely on the notion of global type which specifies the global behaviour and local types, which are the projections of the global behaviour onto each local participant. A central notion in MPST is realisability - whether local implementations derived from a global specification correctly realise the intended protocol under a given communication model. While realisability has been extensively studied under peer-to-peer semantics, it remains poorly understood in alternative communication models such as bag-based, causally ordered, or synchronous communications. In this paper, we develop a unified framework for reasoning about realisability and subtyping across a spectrum of communication models. We show that the communication model does not impact the notion of subtyping, but that it impacts the notion of realisability. We introduce several decision procedures for subtyping checking and realisability checking with complexities ranging from NLOGSPACE to EXPSPACE depending on the assumptions made on the global types, in particular depending on their complementability and the size of a given complement.

Problem

• Investigates realisability of multiparty session types across communication models
• Examines impact of communication semantics on protocol verification and subtyping
• Develops decision procedures for realisability checking under varying complexities

Innovation

• Unified framework for realisability and subtyping across communication models
• Communication model impacts realisability but not subtyping
• Decision procedures with complexities from NLOGSPACE to EXPSPACE