4 Pick an online service that provides certain kinds of social networking service (such as Facebook, twitter, LinkIn, ancestry, ...) as your case studies, and perform some background research to find out the following: (a) For the underlying relation(s) that the social networking service keeps track, how large is the user base (i.e., how many users does the service has)? (Please cite your source). (b) What kind of discovery services does the site provide for its users? (e.g., Facebook suggests possible friends to its users). Make a guess at how it works. 4 (c) Could you suggest new services for the site? Or do you have any hypothesis about the network that is formed using the service (e.g., six-degree of separation)?