How does Lucene compute multifield score?

Question

Here's Lucene scoring equation:

score(q,d) = coord(q,d) · queryNorm(q) · ∑ ( tf(t in d) · idf(t)2 · t.getBoost() · norm(t,d) )

What about multifield scoring?

Does the score gets directly summed or averaged or..?

Answer 1

It depends on the operation. If you are doing an OR as in (name:bill OR gender:male), it takes the max of the two. If you are doing an AND, it will do a sum.

Answer 2

You can read the details of scoring in Similarity class. In this equation, the parameters are referred in reference to Document when they actually mean Field. So, Term Frequency is the frequency of the term in given field in the document. This automatically takes care of the queries on multiple fields.

KenE's answer above is incorrect. (There is no MAX operator in the equation.) The score for each query on a field adds up to the final score. For the query (name:bill OR gender:male) the result is sum of score for (name:bill) and (gender:male). Typically, the documents which satisfy both these criteria will score higher (due to sum) and come up.