This paper investigates a new form of delegation for multiparty session calculi. Usually, delegation allows a session participant to appoint a participant in another session to act on her behalf. This means that delegation is inherently an inter-session mechanism, which requires session interleaving. Hence delegation falls outside the descriptive power of global types, which specify single sessions. As a consequence, properties such as deadlock-freedom or lock-freedom are difficult to ensure in the presence of delegation. Here we adopt a different view of delegation, by allowing participants to delegate tasks to each other within the same multiparty session. This way, delegation occurs within a single session (internal delegation) and may be captured by its global type. To increase flexibility in the use of delegation, our calculus uses connecting communications, which allow optional participants in the branches of choices. By these means, we are able to express conditional delegation. We present a session type system based on global types with internal delegation, and show that it ensures the usual safety properties of multiparty sessions, together with a progress property.

本文研究了一种新的多方会话计算委托形式。通常，委派允许会议参与者指定另一会议的参与者代表她行事。这意味着委派本质上是一种会话间机制，需要会话交织。因此，委派超出了全局类型的描述能力，全局类型指定单个会话。结果，在存在委派的情况下很难确保诸如无死锁或无锁的属性。在这里，我们通过允许参与者在同一多方会话中将任务彼此委派来采用不同的委派观点。这样，委派发生在单个会话中（内部委派），并且可以通过其全局类型捕获。为了增加使用委派的灵活性，我们的演算使用连接通信，允许可选参与者参与选择的分支。通过这些手段，我们能够表达条件委托。我们提出了一种基于具有内部委托的全局类型的会话类型系统，并表明它确保了多方会话的常规安全属性以及进度属性。