In Oracle Database:

The goal is to create a social networks database, like Twitter, where you will store the network (say who-follows-whom) and the associated data of each person like tweets, tags, photos and more. Users should be able to view a chronological listing of anyone's tweets, find tweets by certain people, group tweets by topics, find friends who tweet about some topic, find friends of friends who are not friends (to close social triangles!), and so on