Federated Search Overview
Applies to: SharePoint Server 2010
**Content crawling **In this approach, results are returned from the Search service application’s content index based on the user's query. The content index contains content that is crawled by the Search service application, and includes text content and metadata for each content item.
**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 the search server's own content index.
This topic provides an overview of federated search in SharePoint Enterprise Search.
Comparing Federated Search to Content Crawling in Enterprise Search
To help you decide whether to crawl a repository's content directly or by using federated search, you should consider the differences between the two approaches. You must determine which is most appropriate based on the content repository, and your requirements for the search results you want to return. There are advantages to both approaches.
Advantages of crawling content with SharePoint Enterprise Search
By querying the Search service application's content index for search results, you can do the following:
Sort results by relevance.
Control how frequently the content index is updated.
Specify what metadata is crawled.
Perform a single backup operation for crawled content.
Advantages of federating content with SharePoint Enterprise Search
By using federated search to return search results:
You require no additional capacity requirements for the content index, as content is not crawled by SharePoint Enterprise Search.
You can take advantage of a repository’s existing search engine. For example, you can federate to an Internet search engine to search the Web.
You can optimize the content repository's search engine for the repository's specific set of content, which might provide better search performance on the content set.
You can access repositories that are secured against crawls, but which can be accessed by search queries.
A federated location defines the federated search connection to the external content repository, and is composed of the following:
Query and More Results link templates
Authentication and credentials information
SharePoint Enterprise Search supports the following types of federated locations:
Local Search Index Local SharePoint sites.
FAST IndexFAST Search Server 2010 for SharePoint locations.
OpenSearch 1.0/1.1 The RSS feed for any remote SharePoint site’s results page, or any searchable feed that supports the OpenSearch standard, and returns search results in structured XML format (for example, RSS or Atom results).
You can federate to other repositories by building a lightweight interface that exposes the repository with a searchable XML feed. You can then create an OpenSearch location that connects to the lightweight interface. For more information about how to expose repositories as searchable XML feeds, see Architecture Guidance for Building Federated Search Connectors.
Query and More Results Link Templates
The query template contains the parameterized URL that points to the location's Web interface, and contains the search query and any other parameters that are required by the search engine.
The more results link template contains the URL for an HTML page that displays results for the federated search location.
A trigger is a query constraint that determines when a query is passed. Only queries that match the pattern specified for the triggers in the location definition are forwarded to the federated location. Triggers are essential to the federation experience, as they ensure you display only information that is targeted to the user's query.
There are three types of triggers:
Always An Always trigger always forwards queries to the federated location. If you specify this trigger for the federated location, ensure that the location has enough bandwidth to handle the additional query traffic.
Prefix A prefix trigger contains an exact term, with which the query must be prefixed for the location to match the query. For example, if "weather" is specified as the prefix trigger, then the query "weather New York, NY" will match but only "New York, NY" is forwarded to the federated location.
Pattern A pattern trigger contains a specified regular expression pattern, which the query must match for the trigger to forward the query. To forward only a portion of the query to the federated source, you can create a capture group. The capture group can then be referenced in the query template. For more information on regular expressions and capture groups, see .NET Framework Regular Expressions.
The display information specifies how display the search results that are returned, and includes the following:
The XSLT specifying how to format and render the search results XML.
The list of properties to display in the search results UI.
SharePoint Enterprise Search retrieves all the properties returned for OpenSearch federated locations.
The sample data that is used if you want to edit the results page in Microsoft SharePoint Designer 2010.
You can specify restrictions in the location definition to limit the sites that can use the federated location.
Authentication and Credentials Information
In the authentication and credentials information section of the location definition, you specify the authentication type for the federated location. The authentication type can be one of the following:
Anonymous No credentials are required to connect to the federated location.
Common Each connection uses the same set of credentials to connect to the federated location.
User The credentials of the user who submitted the search query are used to connect to the federated location.
For the common and user authentication types, you must also specify one of the following authentication protocols:
NTLM Application Pool identity (common authentication type only)
Kerberos (user authentication type only)
If the federated location is configured for user authentication and the content repository for the location is on a remote server, you must either use Kerberos authentication or create custom versions of the search Web Parts. These custom versions must include UI elements to request the user's credentials so that they can be passed in the request to the federated location.