Federated Search
Federated search is an information retrieval technology that allows the simultaneous search of multiple searchable resources. A user makes a single query request which is distributed to the search engines participating in the federation. The federated search then aggregates the results that are received from the search engines for presentation to the user.
Purpose
Federated search came about to meet the need of searching multiple disparate content sources with one query. This allows a user to search multiple database at once in real time, arrange the results from the various databases into a useful form and then present the results to the user.
Challenges
When federated search is performed against secure data sources, the users' credentials must be passed on to each underlying search engine, so that appropriate security is maintained. If the user has different login credentials for different systems, there must be a means to map their login ID to each search engine's security domain.[1]
Another challenge is mapping results list navigators into a common form. Suppose 3 real-estate sites are searched, each provides a list of hyperlinked city names to click on, to see matches only in each city. Ideally these facets would be combined into one set, but that presents additional technical challenges.[2] The system also needs to understand "next page" links if it's going to allow the user to page through the combined results.