coord
public abstract float coord(
int overlap,
int maxOverlap
)
Computes a score factor based on the fraction of all query terms that a
document contains. This value is multiplied into scores.
The presence of a large portion of the query terms indicates a better
match with the query, so implemenations of this method usually return
larger values when the ratio between these parameters is large and smaller
values when the ratio between them is small.
idf
public float idf(
Collection terms,
Searcher searcher
)
throws
IOException
Computes a score factor for a phrase.
The default implementation sums the idf(Term,Searcher) factor
for each term in the phrase.
idf
public abstract float idf(
int docFreq,
int numDocs
)
Computes a score factor based on a term's document frequency (the number
of documents which contain the term). This value is multiplied by the
tf(int) factor for each term in the query and these products are
then summed to form the initial score for a document.
Terms that occur in fewer documents are better indicators of topic, so
implemenations of this method usually return larger values for rare terms,
and smaller values for common terms.
idf
public float idf(
Term term,
Searcher searcher
)
throws
IOException
Computes a score factor for a simple term.
The default implementation is:
return idf(searcher.docFreq(term), searcher.maxDoc());
Note that maxDoc() is used instead of
numDocs() because it is proportional to
docFreq(Term) , i.e., when one is inaccurate,
so is the other, and in the same direction.
lengthNorm
public abstract float lengthNorm(
String fieldName,
int numTokens
)
Computes the normalization value for a field given the total number of
terms contained in a field. These values, together with field boosts, are
stored in an index and multipled into scores for hits on each field by the
search code.
Matches in longer fields are less precise, so implemenations of this
method usually return smaller values when numTokens is large,
and larger values when numTokens is small.
That these values are computed under addDocument(Document) and stored then using
{#encodeNorm(float)}. Thus they have limited precision, and documents
must be re-indexed if this method is altered.
queryNorm
public abstract float queryNorm(
float sumOfSquaredWeights
)
Computes the normalization value for a query given the sum of the squared
weights of each of the query terms. This value is then multipled into the
weight of each query term.
This does not affect ranking, but rather just attempts to make scores
from different queries comparable.
sloppyFreq
public abstract float sloppyFreq(
int distance
)
Computes the amount of a sloppy phrase match, based on an edit distance.
This value is summed for each sloppy phrase match in a document to form
the frequency that is passed to tf(float).
A phrase match with a small edit distance to a document passage more
closely matches the document, so implementations of this method usually
return larger values when the edit distance is small and smaller values
when it is large.
tf
public abstract float tf(
float freq
)
Computes a score factor based on a term or phrase's frequency in a
document. This value is multiplied by the idf(Term,Searcher)
factor for each term in the query and these products are then summed to
form the initial score for a document.
Terms and phrases repeated in a document indicate the topic of the
document, so implemenations of this method usually return larger values
when freq is large, and smaller values when freq
is small.
tf
public float tf(
int freq
)
Computes a score factor based on a term or phrase's frequency in a
document. This value is multiplied by the idf(Term,Searcher)
factor for each term in the query and these products are then summed to
form the initial score for a document.
Terms and phrases repeated in a document indicate the topic of the
document, so implementations of this method usually return larger values
when freq is large, and smaller values when freq
is small.
The default implementation calls tf(float).
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