Understanding Score Operators

Every time Verity finds a document, it assigns the document a score that represents how closely the document matches the search criteria. The score is always somewhere from 0 to 1, where 1 is a perfect match and 0 is a perfectly miserable match. In most cases, Verity orders the search results in score order, with the highest scores at the top.

Score operators tell Verity to compute this score differently from what it would do normally. To a certain extent, this allows you to control the order of the documents in the result set. The score operators include the following:

• YESNO

• COMPLEMENT

• PRODUCT

• SUM

The YESNO operator forces the score for any match to be 1, no matter what. In other words, all documents that are relevant at all are equally relevant. The records will not appear in any particular ordereven though Verity is trying to rank the search results by relevancebecause sorting by a bunch of 1s doesn't really do anything. Here is an example:

 CRITERIA="YESNO(policy)" 

The COMPLEMENT operator is kind of strange. This operator subtracts the score from 1 before returning it to you. A closely matching document that would ordinarily get a score of .97 would therefore get a score of only .03. If Verity is ranking records by relevance, using COMPLEMENT makes the search results appear in reverse order (best matches last instead of first). Unfortunately, this also means a score of 0 now has a score of 1, which means that all documents that didn't match at all will be returnedand returned first.

If for some bizarre reason you wanted only documents completely unrelated to smokingranked by irrelevanceyou could use this:

 CRITERIA="<COMPLEMENT>smoking" 

The PRODUCT operator causes Verity to calculate the score for the document by multiplying the scores for each search word found. The net effect is that relevant documents appear even more relevant, and less relevant documents are even less relevant. This operator can cause fewer documents to be found. The following is an example:

 CRITERIA="<PRODUCT>smoking" 

The SUM operator causes Verity to calculate the score for the document by adding the scores for each search word found, up to a maximum document score of 1. The net effect is that more documents appear to get perfect scores. Here is an example:

 CRITERIA="<SUM>smoking">