Microsoft Sync Framework 4.0 CTP is built on top of Sync Framework 2.1. It defines Odata + Sync, a sync protocol that makes it easy to build offline apps on any client platform capable of caching data. The CTP enables synchronization of data stored in Sql Server/Sql Azure over an open standard network format by a remote synchronization service handling all sync specific computations. Moving all synchronization logic off the client enables clients, which don't have SF runtime installed, to cache data and participate in a synchronization topology.
Earlier versions of SF required Windows systems with SF runtime installed on them as clients. This CTP allows other Microsoft platforms such as Silverlight, Windows Phone 7, and Windows Mobile and non-Microsoft platforms such as HTML5, iPhone, Android and other devices with no SF runtime installed on them as clients.
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