Lucene 查询权重排序因子解释（备查）

tf(t in d)：Term frequency factor for the term (t) in the document (d)—howmany times the term t occurs in the document.

idf(t) ：Inverse document frequency of the term: a measure of how“unique” the term is. Very common terms have a low idf; very rare terms have a high idf.

boost(t.field in d): Field and document boost, as set during indexing (see section 2.5).You may use this to statically boost certain fields and certain documentsover others.

lengthNorm(t.field in d): Normalization value of a field, given the number of terms within thefield. This value is computed during indexing and stored in the indexnorms. Shorter fields (fewer tokens) get a bigger boost from this factor.

coord(q, d): Coordination factor, based on the number of query terms thedocument contains. The coordination factor gives an AND-like boost to documents that contain more of the search terms than other documents.

queryNorm(q)： Normalization value for a query, given the sum of the squared weights of each of the query terms.