Sharepoint Search – Federated Search

Microsoft Search Server 2008 provides two approaches for processing queries to return search results:

• Content crawling   In this approach, results are returned from the search server’s content index based on the user’s query. The content index contains content that is crawled by the search server, and includes text content and metadata for each content item. This is the same process that is described for Enterprise Search in Microsoft Office SharePoint Server.
  
• Federated search   In this approach, you are enabled to display search results for additional content that is not crawled by your search server. With federation, the query can be performed over the local content index, or it can be forwarded to an external content repository
  where it is processed by that repository’s search engine. The repository’s search engine then returns the results to the search server. The search server formats and renders the results from the external repository within the same search results page as the results from search server’s own content index. (Open Search 1.0/1.1)