With the ubiquitous adoption of the World Wide Web, an overwhelming amount of high quality, structured data becomes available on the Web. Unlike in the traditional context, Web databases are directly accessible by end users. To help ordinary users overcome the information overload in structured data, current databases need to improve the usability as well as the querying capability. This book explores this direction by discussing how to support novel, user-friendly query types in existing data management systems and investigating techniques for enabling efficient and scalable implementations of these query operators.