Linked is popular social networking sit, more of business and professional connections.
In using this linkedin you have have seen the great features like following
1. "who viewed my profile"
2. "Jobs you may be interested"
Have been researching (rather searching on web), but it is difficult to get what is scope of these "use cases". Over the years Linked in has changed architecture drastically.
This very tricky, you need to use OLAP and computers to capture data.
This uses mix of linked technology, there are various papers/videos which explain. The overall block diagram is as follows:
1. Offline engines to compute in batch mode
2. Online engine queries in online.
For more details : Avatara: OLAP for Web-scale Analytics Products
1. Hadoop engine
2. Voldermort (same name as developer is fan of Harry Potter)