Mediating and Metasearching on the Internet

The Internet emerges as the largest database. Increasingly, users want to issue complex queries across Internet sources to obtain the data they require. However, finding relevant information sources and querying them manually is problematic: there are numerous sources, and they vary in the type of information objects they contain and in the interface they present to their users. Some sources contain text documents and support simple query models where a query is just a list of keywords. Other sources contain more structured data and provide query interfaces in the style of relational query languages. Furthermore, users have to manually fuse the query results by merging information, removing redundancies, ranking the answer objects in the appropriate order, and so on. Since it is tedious to contact several heterogeneous sources, users can benefit from metasearchers and mediators, which are services that provide users with a virtual integrated view of the heterogeneous sou