The subject invention pertains to systems and methods of data item synchronization. More specifically, the invention concerns synchronization of data entities utilizing an intermediary or shared storage system and associated data store. Each client sync device can include or be associated with an interface that facilitates communication between client synchronization devices and the intermediary storage system. The interface can send change information to the shared store utilizing change data packets including a data change attribute, a prerequisite knowledge attribute and a learned knowledge attribute. The data change attribute can specify changes to be made to certain data, while the attribute can include a complete copy or reference to a complete copy or single instance of data.