Adding a Weight to Boost or Lower the Relevance of an Included Element
When you include an element, one of the options is to add a weight to the included element specification. When you add a weight, all text in this element (including any text in all text node descendants of the element) are weighted by the specified value, changing the relevance at query time. Specifying a weight greater than 1.0 will boost scores and a weight lower than 1.0 will lower scores for matches within the element.
When you specify a weight, the term frequency for any tokens in that element (including tokens in descendant text nodes) is multiplied by that number. This happens during document load, update, or reindexing. For example, if you specify a weight of 2.0, each term will have a term frequency of 2.0, making it as if each term appeared twice (for score calculation purposes). Similarly, if you specify a weight of 0.5, each term will have a term frequency of 0.5.
Note
Because the weight boosting affects term frequency, it will only affect relevance orders for scoring algorithms that include term frequency (for example, logtf/idf or logtf); scoring algorithms that do not consider weight will not be affected by these weights (for example, score-simple).
Adding a weight is useful to boost or lower scores on searches where the match occurs in a given element. For example, if you want matches in TITLE elements to contribute more towards the relevancy score than matches in other elements, you can specify a weight of 2.0 for the TITLE element. Conversely, if you want matches in TITLE elements to contribute less to the relevancy score than matches in other elements, you can specify a weight of 0.5 for the TITLE element. For details on how relevance is calculated, see Composing cts:query Expressions in the Search Developer’s Guide.