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From John Wang <john.w...@gmail.com>
Subject Re: Proposal: Scorer api change
Date Tue, 08 Jun 2010 16:02:48 GMT
Hi Shai:

    I am not sure I understand how changing Similarity would solve this
problem, wouldn't you need the reader?

    As for PayloadTermQuery, payload is not always the most efficient way of
storing such data, especially when number of terms << numdocs. (I am not
sure accessing the payload when you iterate is a good idea, but that is
another discussion)

    Yes, what I described is exactly a simple CustomScoreQuery for a special
use-case. The problem is also in CustomScoreQuery, where nextDoc and advance
are calling the sub-scorers as a wrapper. This can be avoided if the Scorer
returns an iterator instead.

    Separating scoring and doc iteration is a good idea anyway. I don't know
the reason to combine them originally.

Thanks

-John

On Tue, Jun 8, 2010 at 8:47 AM, Shai Erera <serera@gmail.com> wrote:

> So wouldn't it make sense to add some method to Similarity? Which receives
> the doc Id in question maybe ... just thinking here.
>
> Factoring Scorer like you propose would create 3 objects for
> scoring/iterating: Scorer (which really becomes an iterator), Similarity and
> CustomScoreFunction ...
>
> Maybe you can use CustomScoreQuery? or PayloadTermQuery? depends how you
> compute your age decay function (where you pull the data about the age of
> the document).
>
> Shai
>
>
> On Tue, Jun 8, 2010 at 6:41 PM, John Wang <john.wang@gmail.com> wrote:
>
>> Hi Shai:
>>
>>     Similarity in many cases is not sufficient for scoring. For example,
>> to implement age decaying of a document (very useful for corpuses like news
>> or tweets), you want to project the raw tfidf score onto a time curve, say
>> f(x), to do this, you'd have a custom scorer that decorates the underlying
>> scorer from your say, boolean query:
>>
>> public float score(){
>>     return myFunc(innerScorer.score());
>> }
>>
>>     This is fine, but then you would have to do this as well:
>>
>> public int nextDoc(){
>>    return innerScorer.nextDoc();
>> }
>>
>> and also:
>>
>> public int advance(int target){
>>    return innerScorer.advance();
>> }
>>
>>      The difference here is that nextDoc and advance are called far more
>> times as score. And you are introducing an extra method call for them, which
>> is not insignificant for queries result in large recall sets.
>>
>> Hope this makes sense.
>>
>> Thanks
>>
>> -John
>>
>> On Tue, Jun 8, 2010 at 5:02 AM, Shai Erera <serera@gmail.com> wrote:
>>
>>> I'm not sure I understand what you mean - Scorer is a DISI itself, and
>>> the scoring formula is mostly controlled by Similarity.
>>>
>>> What will be the benefits of the proposed change?
>>>
>>> Shai
>>>
>>>
>>> On Tue, Jun 8, 2010 at 8:25 AM, John Wang <john.wang@gmail.com> wrote:
>>>
>>>> Hi guys:
>>>>
>>>>     I'd like to make a proposal to change the Scorer class/api to the
>>>> following:
>>>>
>>>>
>>>> public abstract class Scorer{
>>>>    DocIdSetIterator getDocIDSetIterator();
>>>>    float score(int docid);
>>>> }
>>>>
>>>> Reasons:
>>>>
>>>> 1) To build a Scorer from an existing Scorer (e.g. that produces raw
>>>> scores from tfidf), one would decorate it, and it would introduce overhead
>>>> (in function calls) around nextDoc and advance, even if you just want to
>>>> augment the score method which is called much fewer times.
>>>>
>>>> 2) The current contract forces scoring on the currentDoc in the
>>>> underlying iterator. So once you pass "current", you can no longer score.
In
>>>> one of our use-cases, it is very inconvenient.
>>>>
>>>> What do you think? I can go ahead and open an issue and work on a patch
>>>> if I get some agreement.
>>>>
>>>> Thanks
>>>>
>>>> -John
>>>>
>>>
>>>
>>
>

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