SSE defines new XML elements that add replication information to items in an RSS feed and so implement bidirectional RSS. That is two endpoints can mutually publish and subscribe to each other's RSS feed, when changes are made in one endpoint, they are propagated to the other and vice versa.
These new XML elements also enable feed readers and publishers to generate and process incoming item changes in a manner that enables consistency to be achieved by change histories (to manage item versions and update conflicts) and tombstones (to propagate deletions, and un-deletions).
Read all about it in Ray's blog.
From the FAQ:
What kinds of scenarios does SSE enable?
- Just as RSS enables the aggregation of information from a variety of data sources, SSE enables the replication of information across a variety of data sources. Data sources that implement SSE will be able to exchange data with any other data source that also implements SSE.
- From the user's perspective, this means that you will be able to share your data (such as calendar appointments, contact lists, and favorites) across all of your devices and with anyone else that you choose, regardless of infrastructure or organization.
- SSE is particularly useful for scenarios in which there are multiple masters and/or asynchronous updates. For example, SSE could be used to share your work calendar with your spouse—either of you could enter new appointments, even if not currently connected. Similarly, SSE could be used to replicate a set of calendar entries among a group of people, each working in a different company and using different infrastructure.