“The social graph is only one instance of a class of data structure that will prove increasingly important as we build applications powered by data at internet scale. You can think of the mapping of people, businesses, and events to places as the ‘location graph’, or the relationship of search queries to results and advertisements as the ‘question-answer graph.’”
–Tim O’Reilly
[...] A1: The “social graph,” the “location graph,” and the “question-answer” graph. [...]