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Amazon CloudSearch
Developer Guide (API Version 2013-01-01)

Using Relative Field Weighting to Customize Relevance Ranking in Amazon CloudSearch

You can assign weights to selected fields so you can boost the relevance _score of documents with matches in key fields such as a title field, and minimize the impact of matches in less important fields. By default all fields have a weight of 1.

Field weights are set with the q.options fields option. You specify fields as an array of strings. To set the weight for a field, you append a caret (^) and a positive numeric value to the field name. You cannot set a field weight to zero or use mathematical functions or expressions to define a field weight.

For example, if you want matches within the title field to score higher than matches within the plot field, you could set the weight of the title field to 2 and the weight of the plot field to 0.5:

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q.options={fields:['title^2','plot^0.5']}

In addition to controlling field weights, the fields option defines the set of fields that are searched by default if you use the simple query parser or don't specify a field in part of a compound expression when using the structured query parser. For more information, see Search Request Parameters in the Search API Reference.

To reference the weighted relevance score in the definition of an expression, you use _score. You can use the weighted _score value in conjunction with numeric fields, other expressions, and the standard numeric operators and functions. For more information, see Configuring Expressions.