Rank Profile

You use a rank profile to specify how to perform relevance ranking of query results. For more information about the rank profile concepts, see About the Rank Profile (FAST Search Server 2010 for SharePoint) on Microsoft TechNet.

The rank profile is configured to calculate the rank score with input from quality rank components (also known as static rank components) and dynamic rank components. The default rank profile is named default, which is also used as the default sort criteria (Sort by Relevance) on the search result page. Be aware that you tune rank components independently of one another. The value of two rank components with the same weight is not necessarily the same so that changing a weight from 50 to 100 on one component could lead to more effect on the final rank score than changing a weight from 50 to 100 on another component.

A rank profile is associated with one or more full-text indexes for full-text query rank evaluation.

You typically have a one-to-one relation between a full-text index and a rank profile. In some applications, you might want to group the text content in more than one full-text index. To rank queries by relevance, regardless of which full-text index is specified in the query, you must have all the full-text indexes mapped to the rank profile used for the query.

The following example shows why you would want to have two full-text indexes and map them to the same rank profile. In your application, you have a set of managed properties that represents the visible content of the item, such as title, body, and headings. You map these properties to the full-text index named content (the default full-text index). Then, you can control the relevance importance of each property when the user queries this full-text index. You may also have a set of managed properties that represent tags and annotations added by users. To enable the user to apply free-text queries toward these properties, you map these properties to another full-text index that is named annotations. If you map both full-text indexes to a rank profile, you can ensure that the following query is correctly relevance ranked:

new movies annotations:cool

A rank profile can be associated with one or more managed properties for quality rank evaluation. Each managed property is associated with the full-text index by using a weight to describe the relative weight of this managed property in the overall quality rank computation.

Note :
A default index schema configuration contains one rank profile named default, which is the default rank profile for queries without any rank profile specification.

Rank profile tuning involves the following factors: quality, authority, query authority, freshness, proximity, context, and managed property. These are described in Table 4. You can specify relative weight for the individual components in a rank profile.

Ranking Factors:

Rank Factor	Description
Quality	Specifies the quality score, also known as the static rank score. Static rank can be derived from multiple managed properties. The following sets of managed properties are predefined for static ranking: Urldepthrank    Used to boost shorter URLs. Docrank    Rank boost based on the number of and relative importance of links pointing to an item. Siterank    Rank boost based on the number of and relative importance of links pointing to the items on a site. Hwboost    FAST Search Server 2010 for SharePoint placeholder for generic usage of static rank points. In addition to these predefined static rank properties, you can add any custom integer managed property to the list of static rank managed properties by using the QualityComponent interface. This interface also enables you to assign different relative weights to the individual components.
Authority	Specifies the rank given when a query word retrieves hits in the link text (anchor text). This score has two components: Partial match of the link text. For example, if a user makes a query Microsoft, and the link text is Microsoft Word, you get a partial match rank score for this item. Complete match of the link text. An additional score is added if there is an exact match between the query text and the link text.
Query authority	Specifies the rank given when a new query retrieves hits in items that are associated with previously performed queries. In the search UI, all of a user's queries and the items that the user clicks on that are associated with those queries are stored and processed. This factor enables users to affect the relevance ranking of frequent queries through the items in the query result that they click on. Processing occurs one time each day at 01:00 AM. The last 30 days of clicks are kept for processing. This rank boost has two components: Partial match. For example, if the initial query that resulted in a click to this item is Microsoft Word, and the query is Microsoft, you will get a partial match rank score for this item. Complete match. Another score is added if there is an exact match between the user query and the stored query authority query.
Freshness	Specifies the freshness boost that is assigned to an item based on the last modified time for the item compared to the time of the query. The source for the last modified time is the managed property named Write. You specify the resolution by using the RankProfile.FreshnessResolution property. A lower resolution implies that smaller time differences will affect the ranking.
Proximity	Specifies the proximity boost that is assigned to an item depending on the distance between the query words in the item, and where the words are located in the item. Proximity boost is based on distance between terms inside a full-text index. You get a larger boost if two terms appears in the same managed properties within the full-text index. You can use the RankProfile.PositionStopWordThreshold property to configure how to apply proximity ranking to frequent query words. For more information, see RankProfile.
Context	Specifies a boost that depends on where in the item the search words hit. Context boost is assigned as an overall weight and as a weight based on the different levels defined in the full-text index. The different managed properties such as title and body are mapped into different levels. This makes it possible to give a better rank score when the search word hits on a title instead of in the body text of the item. For more information, see Importance Level and Drilling.
Managed property boost	Specifies a rank component that enables an administrator to boost indexed items based on a word match with a managed property. Any searchable managed property that has a matching value can be used as input for additional rank points. For example, you may want to boost indexed items of a specific type (such as Microsoft Word documents). You specify the boost by using the ManagedPropertyBoostComponent interface. In this example, the condition will be that the managed property fileextension must have the value doc or docx.

Note:

Both the quality boost and managed property boost provide rank boost that is independent of the actual query. A quality boost provides an unconditional boost for all items in a result set that contains any nonzero value in the associated numeric managed property. The boost value is equal to the numeric value of the property for each matching item in the index. A managed property boost provides a conditional boost for all items where the indicated managed property matches one or more specific words. The matching is performed during query evaluation. You specify the matching condition and the boost value in the ManagedPropertyBoostComponent.BoostValue property.

Rank profile related interfaces :

Interface	Description
RankProfile	Specifies a rank profile.
RankProfileCollection	Enables access to an existing rank profile. You use the RankProfileCollection.Create method to create a new rank profile.
FullTextIndex	A full-text index enables you to query across several managed properties at the same time. You can map one or more full-text indexes to the rank profile by using the RankProfile.GetFullTextIndexRanks method.
FullTextIndexMapping	Maps one managed property to a full-text index. The ImportanceLevel property defines the relative importance of this managed property within the full-text index. This is used in the context boost evaluation when the full-text index is associated with a rank profile. For more information, see Importance Level and Drilling.
ManagedProperty	Managed properties are metadata that can be searched or retrieved in query results. You can associate a managed property boost configuration with a rank profile by using the RankProfile.GetManagedPropertyBoosts method. You can associate one or more managed properties for quality ranking (static ranking) to a rank profile by using the RankProfile.GetQualityComponents method.
QualityComponent	Associates one or more managed properties for quality ranking. You manage the association by using the RankProfile.GetQualityComponents method.
ManagedPropertyBoostComponent	Associates a managed property boost configuration with a rank profile. You manage the association by using the RankProfile.GetManagedPropertyBoosts method.
FullTextIndexRankComponent	Associates one or more full-text indexes to the rank profile. You manage the association by using the RankProfile.GetFullTextIndexRanks method. For more information, see Importance Level and Drilling.