During Strong Angel II in 2004, Steve Birch, Steve Price and I conducted a series of experiments around a concept we called The Pony Express, which involved the use of Groove-based “mobile infrastructure” to deliver data synchronization services to users beyond the horizon of connectivity. For Strong Angel III, we will revisit the concept using the neutral, platform independent SSE replication protocol. First, I’d like to set the stage with a bit of background on the problem we were originally setting out to address.

In November of 2005, then Microsoft CTO Ray Ozzie proposed a set of extensions to RSS that would allow the protocol to support replication of structured data between loosely-coupled applications. The concept was simple: just as RSS feeds may be used to publish and subscribe to news articles, contact lists, or calendars. so SSE could allow one or more systems containing stories, vcards, and events to be cross-subscribed with one another. When two or more SSE feeds are cross-subscribed, their contents merge and replicate all changes to each endpoint. SSE is, in effect, bi-directional RSS; it extends RSS by adding semantics to track changes made at each endpoint and an algorithm for resolving conflicts. When multiple SSE endpoints become cross-subscribed, the result is a kind of application mesh, in which data is replicated between any number of systems.