5. The method of claim 3 comprising: determining a category for the second link is the second category type, different from the first category type; and in the social graph, creating a second edge between the first and second nodes, wherein the second edge is representative of the second category type
3. The method of claim 2 comprising: receiving third activity information for the sender of a second link to the recipient collected by a collection resource at a Web site; and receiving fourth activity information when the recipient accesses the second link sent by the sender corresponding to the third activity information stored at the storage server.