I think we need to be careful not to confuse people by overloading the term "node".

Maybe we need to refer to the node property of the SNMI as the "node item" exclusively, and this section could be made more precise as well.  Something like: "Each instance of related data cached by the SNI is related to a particular Node.  That Node represents a view of data in the social graph and consists of: an item identifier, the type of that item, and the filters that define which data from the graph will be retrieved (known as the related data).  One or more SocialNetworkModelInterface instances may present data associated with a particular Node simultaneously."