Situation-aware Group Communication Protocols

In distributed systems, a group of multiple processes are cooperating with each other through networks. A process is modeled to be a sequence of events in a finite state machine model. Here, it is significant to decide on which event occurs before another event for a pair of events in a system. In the famous happened-before relation among events, events are ordered on the basis of send-receive semantics of messages. Only events which are meaningful in distributed applications should rather be causally ordered, i.e. events which occur in some situation. We consider publish/subscribe (PS) systems which are event-driven systems and are used in various distributed applications. The causal order of events is important to be discussed in a situation where the events meaningfully occur. We consider a peer-to-peer (P2P) model of a publish/subscribe system (P2PPS) where every peer process (peer) can publish events, subscribe events, and is notified of events. There are subscribing, publishing, and notifying events in P2PPS systems. In this paper, we discuss a situation-aware causal dependency of application events in a P2PPS system.