NISO and the Open Archives Initiative have released ResourceSync Framework Specification—Beta Draft.
Here's an excerpt:
This ResourceSync specification describes a synchronization framework for the web consisting of various capabilities that allow third party systems to remain synchronized with a server's evolving resources. The capabilities can be combined in a modular manner to meet local or community requirements. The specification also describes how a server can advertise the synchronization capabilities it supports and how third party systems can discover this information. The specification repurposes the document formats defined by the Sitemap protocol and introduces extensions for them.