Sometimes you cannot or do not want to use the SharePoint 2010 search engine for some content sources but still want to return search results from that content. For this scenario, you can consume search results from a federated source.
Federation can be configured from locations that are OpenSearch 1.0/1.1-compatible and can return with RSS or Atom of the result set.
The following is a list of circumstances when federation needs to be used:
• The content source is huge, and you don’t want to build your own index of it (for example, MSDN, or Wikipedia sites).
• The content in the source changes often, and you need immediate crawling instead of SharePoint’s scheduled crawling.
• The queries have to be processed under a different ...