Social Networking backend architecture

Question

Ideally, where would an application like Facebook store its \"Friends\" data? In a database table? in an xml file?

Answer 1

Most probably it should contain some other mechanism. As an example a search engine does not keep its index as a database or XML file. To obtain a maximum performance generally they keep some tree (Binary search tree or more complicated one) and store them on disk in performance effective manner. So I guess such mechanism.