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From Rebecca Watson <bec.wat...@gmail.com>
Subject Re: about norm
Date Wed, 02 Jun 2010 08:26:29 GMT
There are index time boosts ie calculated at index time and search
time boosts. The field f always relates to the field(s) that the term
t appears in.

My understanding is that--
Norm(t,d) includes the index time boosts for each field but I think t
is only included in this calc in terms of field.getboost() -- because
you effectively get the product over each field in which the specific
term occurs. But you don't have s norm value for e every term- field -
doc combo.

Similarity (defaultsimilarity by default!) method computeNorm is used
to compute this factor at indexing time so have a look at that code to
see what I mean!

IndexReader.norms(fieldname) gives a norm array the size of the number
of docs so norm[docid] is actually used to get the index time boost
for the given field/doc in which the term occurs.

t.getboost() is the search time boost for the particular term --
practically this is the query boost for the term (or I think product
of query boosts if the term is also a sub- query (where the
surrounding query has a query boost too).

I may be wrong but when I dug into the docs + code these were my
conclusions!

bec :)

Sent from my iPhone

On 02/06/2010, at 3:19 PM, Li Li <fancyerii@gmail.com> wrote:

> in javadoc http://lucene.apache.org/java/2_4_0/api/org/apache/lucene/search/Similarity.html#formula_norm
> norm(t,d)   =   doc.getBoost()  ·  lengthNorm(field)  ·   ∏
> f.getBoost()
>                                                                field
> f in d named as t
> whre is field come from in lengthNorm(field)?
> In my option, term t may appear in a doc d many times with different
> fields. So
>       ∏  f.getBoost()
> field f in d named as t
> makes sense.
> But Why there is only one lengthNorm(field) ?
> does it mean that norm(t,d)=norm(t.text, t.field, d)? That's is--
> every doc,every field,every term , there is a norm value ?
>
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