Multiparty session types (MSTs) are a type-based approach to verifying communication protocols, represented as global types in the framework. We present a precise subtyping relation for asynchronous MSTs with communicating state machines (CSMs) as implementation model. We address two problems: when can a local implementation safely substitute another, and when does an arbitrary CSM implement a global type? We define safety with respect to a given global type, in terms of subprotocol fidelity and deadlock freedom. Our implementation model subsumes existing work which considers local types with restricted choice. We exploit the connection between MST subtyping and refinement to formulate concise conditions that are directly checkable on the candidate implementations, and use them to show that both problems are decidable in polynomial time.

中文翻译：

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决定异步多方会话的子类型

多方会话类型 (MST) 是一种基于类型的方法，用于验证通信协议，在框架中表示为全局类型。我们提出了一种以通信状态机 (CSM) 作为实现模型的异步 MST 的精确子类型关系。我们解决两个问题：本地实现何时可以安全地替代另一个本地实现，以及任意 CSM 何时实现全局类型？我们根据子协议保真度和死锁自由度来定义给定全局类型的安全性。我们的实施模型包含了考虑本地类型且选择有限的现有工作。我们利用 MST 子类型和细化之间的联系来制定可在候选实现上直接检查的简明条件，并使用它们来表明这两个问题都可以在多项式时间内判定。