I am talking about the title field. And for the title field, a sweetspot interval of 1 to 50 makes very little sense. I want to have a fieldNorm value that differentiates between for example 2, 3, 4 and 5 terms in the title, but only very little.
The 20% number I got by simply calculating the difference in the title fieldNorm of two documents, where one title was one word longer than the other title. And one fieldNorm value was 20% larger then the other as a result of that. And since we use multiplicative scoring calculation, a 20% increase in the fieldNorm results in a 20% increase in the final score. I'm not talking about "scores as percentages". I'm simply noting that this minor change in the text data (adding or removing one single word) causes the score to change by a almost 20%. I noted this when I renamed a document, removing a word from the title, and that single change caused the document to move up several positions in the result list. We don't want such minor modifications to have such big impact of the resulting score. I'm not sure I can agree with you that "the effect of document length normalization factor is minimal". Then why does it inpact our result in such a big way? And as I said, we don't want to disable it completely, we just want it to have a much lesser effect, even on really short texts. /Jimi ________________________________________ From: Ahmet Arslan <iori...@yahoo.com.INVALID> Sent: Thursday, April 21, 2016 12:10 AM To: solr-user@lucene.apache.org Subject: Re: Is it possible to configure a minimum field length for the fieldNorm value? Hi Jimi, Please define a meaningful document-lenght range like min=1 max=50. By the way you need to reindex every time you change something. Regarding 20% score change, I am not sure how you calculated that number and I assume it is correct. What really matters is the relative order of documents. It doesn't mean anything addition of a word decreases the initial score by x%. Please see : https://wiki.apache.org/lucene-java/ScoresAsPercentages There is an information retrieval heuristic which says that addition of a non-query term should decrease the score. Lucene's default document length normalization may favor short document too much. But folks blend score with other structural fields (popularity), even completely bypass relevancy score and order by price, production date etc. I mean there are many use cases, the effect of document length normalization factor is minimal. Lucene/Solr is highly pluggable, very easy to customize. Ahmet On Wednesday, April 20, 2016 11:05 PM, "jimi.hulleg...@svensktnaringsliv.se" <jimi.hulleg...@svensktnaringsliv.se> wrote: Hi Ahmet, SweetSpotSimilarity seems quite nice. Some simple testing by throwing some different values at the class gives quite good results. Setting ln_min=1, ln_max=2, steepness=0.1 and discountOverlaps=true should give me more or less what I want. At least for the title field. I'm not sure what the actual effect of those settings would be on longer text fields, so maybe I will use the SweetSpotSimilarity only for the title field to start with. Of course I understand that there are many things that can be considered domain specific requirements, like if to favor/punish short/medium/long texts, and how. I was just wondering how many actual use cases there are where one want's a ~20% difference in score between two documents, where the only difference is that one of the documents has one extra word in one field. (And now I'm talking about an extra word that doesn't affect anything else except the fieldNorm value). I for one find it hard to find such a use case, and would consider it a very special use case, and would consider a more lenient calculation a better fit for most use cases (and therefore most domains). :) /Jimi -----Original Message----- From: Ahmet Arslan [mailto:iori...@yahoo.com.INVALID] Sent: Wednesday, April 20, 2016 8:14 PM To: solr-user@lucene.apache.org Subject: Re: Is it possible to configure a minimum field length for the fieldNorm value? Hi Jimi, SweetSpotSimilarity allows you define a document length range, so that all documents in that range will get same fieldNorm value. In your case, you can say that from 1 word up to 100 words do not employ document length punishment. If a document is longer than 100 do some punishment. By the way; favoring/punishing short, middle, or long documents is domain specific thing. You are free to decide what to do. Ahmet On Wednesday, April 20, 2016 7:46 PM, "jimi.hulleg...@svensktnaringsliv.se" <jimi.hulleg...@svensktnaringsliv.se> wrote: OK. Well, still, the fact that the score increases almost 20% because of just one extra term in the field, is not really reasonable if you ask me. But you seem to say that this is expected, reasonable and wanted behavior for most use case? I'm not sure that I feel comfortable replacing the default Similarity implementation with a custom one. That would just increase the complexity of our setup and would make future upgrades harder (we would for example have to remember to check if the default similarity configuration or implementation changes). No, if it really is the case that most people like and want this, and there is no way to configure Solr/Lucene to calculate fieldNorm in a more reasonable way (in my book) for short field values, then I just think we are forced to set omitNorms="true", maybe in combination with a simple field boost for shorter fields. /Jimi -----Original Message----- From: Jack Krupansky [mailto:jack.krupan...@gmail.com] Sent: Wednesday, April 20, 2016 5:18 PM To: solr-user@lucene.apache.org Subject: Re: Is it possible to configure a minimum field length for the fieldNorm value? FWIW, length for normalization is measured in terms (tokens), not characters. With TDIFS similarity (the default before 6.0), the normalization is based on the inverse square root of the number of terms in the field: return state.getBoost() * ((float) (1.0 / Math.sqrt(numTerms))); That code is in ClassicSimilarity: https://github.com/apache/lucene-solr/blob/releases/lucene-solr/5.5.0/lucene/core/src/java/org/apache/lucene/search/similarities/ClassicSimilarity.java#L115 You can always write your own custom Similarity class to override that calculation. -- Jack Krupansky On Wed, Apr 20, 2016 at 10:43 AM, <jimi.hulleg...@svensktnaringsliv.se> wrote: > Hi, > > In general I think that the fieldNorm factor in the score calculation > is quite good. But when the text is short I think that the effect is two big. > > Ie with two documents that have a short text in the same field, just a > few characters extra in of the documents lower the fieldNorm factor too much. > In one test the text in document 1 is 30 characters long and has > fieldNorm 0.4375, and in document 2 the text is 37 characters long and > has fieldNorm 0.375. That means that the first document gets almost a > 20% higher score simply because of the 7 character difference. > > What are my options if I want to change this behavior? Can I set a > lower character limit, meaning that all fields with a length below > this limit gets the same fieldNorm value? > > I know I can force fieldNorm to be 1 by setting omitNorms="true" for > that field, but I would prefer to still have it, just limit its effect > on short texts. > > Regards > /Jimi > > >
