WHAT IS A FEDERATED DATABASE?
A federated database is a collection of data stored on multiple autonomous computing systems connected by a network that is presented to users as one integrated database. A federated database presents data to users by means of user views that, from a user perspective, look exactly like the views of data in a centralized database. User views in a federated database are mapped to underlying tables or objects that may be stored on any of the various databases in the federation. The federated database system processes queries defined in terms of these views, retrieving data as needed from the other systems in the federation, and delivering the results as if all the data was local. Anyone who uses the Internet takes the delivery of content from multiple systems for granted. Almost every Web page on a major commercial site is assembled automatically from multiple sources. Click on a button and data may be retrieved from other databases and servers. Users may not be aware of this, but it goes
