A search tool designed to query multiple networked information resources via a single interface (example: Google Scholar). The metasearch engines developed in the second half of the 1990s were capable of searching only publicly accessible Web sites, but the 21st century has seen a new generation of federated search engines designed to search local and remote library catalogs, subscription databases, and digital repositories as well as Web sites, using standardized protocols, such as Z39.50. Some federated search systems provide deduping and rank results by relevance or allow sorting by other criteria. Limiting, advanced search modes, clustering, and RSS feeds or search alerts may also be available.