Data structure in web development

how the large social networking sites stor开发者_如何学Ce data such as friend list...is it possible to implement data structures such as tree using xml or any other language

how the large social networking sites store data such as friend list

There is a huge shift towards schemaless/NoSQL/document-oriented databases these days, that support the scenario you mentioned without losing scalability and perform well under high loads.

You might want to have a look at a few to better understand the concept. You can start with Mongodb, apache couchdb, google BigTable/datastore (through app engine), and many others as per your need.