CMS 10.6 Boost Multipliers
InSite Search achieves fast search responses because of the way its Lucene engine searches indexes rather than individually searching each unit of content. Lucene uses a predefined formula to score and rank each matched page or other content source. Administrators can "boost" the relevance of defined content so that the content gains more prominence in search results.
Boosts
Boost values are set for page types and fields before they are indexed. Boosting provides a way to adjust the search relevance of InSite Search results. This feature tunes the search results by changing the components in the scoring formula. Boost values affect the calculation of the total document score when ranking documents that match search criteria. When CMS administrators boost a field, the content containing the boosted field will rank higher than other matching content in the score calculation formula, provided all other factors are equal.
Configuring a boost value is an index-time event in InSite Search. This means that any changes to boost values will require a re-indexing of search content. We recommend that administrators create test environment to test these changes in search results prior to making the changes in a live production environment.
Scoring
Boost values are configured as a float value, defaulting to a value of 1.0. In the score calculation formula, the boost number is multiplied by other numeric factors, so the boost default value of 1.0 has the effect of ignoring boost considerations. When the boost value is set to a number greater than 1.0, the final score increases. You can view the tallied score value within the Score element of a search result's XML data.
Assuming no other influences are in place, a boost value of 2.0 will rank a field higher than another field with a boost value of 1.5. For example, page type Alpha has a boost value of 2.0 on its Title field; whereas, page type Beta has a boost value of 1.5 on its Title field. A user runs a query with Product as the search term. Page instances built from both Alpha and Beta schemas return, because the term Product is present in all Title fields of the returned pages. If all else is equal, the pages of type Alpha will rank in the result set higher than Beta's because of the higher boost value applied to the field.
However, it's an over-simplification to say that high boost number values result in high ranks within the results set. Keep in mind that boosting is also dependent on factors such as how often the search term occurs in the boosted field. The total score of the calculation formula determines the ultimate ranking of content within the result set.
- While you can set the boost value from a range of 1.0 through 4.0, the recommended range is to stay within 1.0 through 2.0, as higher values tend to introduce additional variances in results.
- Lucene search rounds boost values to the nearest .25 increment. For example, if you set the boost value to 1.3, then Lucene search rounds the value to 1.25. If you set the boost value to 1.1, the Lucene search rounds the value to 1.0.
Ranking
Administrators could increase the boost field value because the default score algorithm does not accurately reflect the "relevance order" of content units. For example, let's suppose there are five pages, each with a Title field. Prior to setting a boost value, the page ranking order is [x1, x2, x3, x4, x5]. If administrators increase the Title field boost of x5 at index time, then for the same search, x5 will move up in search results ranking.
Recap
Lucene search has three distinct phases:
- Lucene builds an index based on defined content.
- Lucene finds documents that match users search criteria.
- Lucene calculates the score for each search result and assigns rank.
Boosting page types and fields influence the overall score formula. Boost values greater than 1.0 push the most relevant content towards the top of search results.