Our world is networked: people are closer to each other through online social network services or mobile communication networks, while information is capable to be exchanged faster by World Wide Web or email networks. The network is a treasure trove of user experiences and knowledge that presents great opportunities to understand the fundamental science of our world. On the other hand, the network, with huge amount of data, and multiple types of entities (e.g., users, documents, organizations, etc.), user behaviors, and relations between entities, has become so large and complex that traditional methodologies are inadequate.