Yes. Boosting adjusts an existing score. That original score can vary, e.g. depending upon how many search terms there are.
If you use additive boosting, when you add a boost to a search with one term, (e.g. between 0 and 1) you get a different effect compared to when you add the same boost to a search with four terms (e.g. between 0 and 4). If, however, you used multiplicative boosting, the impact of the boosts would be the same. If, for example, you want to add a recency boost, say with recip, where the boost value is between 0 and 1, then use score*(1+boost). This way, a boost of 0 has no effect on the score, whereas a boost of 1 doubles the score. If you use plain multiplicative here, a boost of 0 wipes out the score entirely, which can have nasty effects (it has, at least, for me). Upayavira On Thu, 17 Mar 2016, at 06:58 PM, Walter Underwood wrote: > Think about using popularity as a boost. If one movie has a million > rentals and one has a hundred rentals, there is no additive formula that > balances that with text relevance. Even with log(popularity), it doesn’t > work. > > With multiplicative boost, we only care about the difference between the > one rented one million time and the one rented 800 thousand times (think > about the Twilight movies at Netflix). But it also distinguishes between > the one rented 100 times and the one rented 80 times. > > wunder > Walter Underwood > wun...@wunderwood.org > http://observer.wunderwood.org/ (my blog) > > > > On Mar 17, 2016, at 11:29 AM, jimi.hulleg...@svensktnaringsliv.se wrote: > > > > Hi, > > > > After reading a bit on various sites, and especially the blog post > > "Comparing boost methods in Solr", it seems that the preferred boosting > > type is the multiplicative one, over the additive one. But I can't really > > get my head around *why* that is so, since in most boosting problems I can > > think of, it seems that an additive boost would suit better. > > > > For example, in our project we want to boost documents depending on various > > factors, but in essence they can be summarized as: > > > > - Regular edismax logic, like qf=title^2 mainText^1 > > - Multiple custom document fields, with weights specified at query time > > > > So, first of, the custom fields... It became obvious to me quite quickly > > that multiplicative logic here would totally ruin the purpose of the > > weights, since something like "(f1 * w1) * (f2 * w2)" is the same as "(f1 > > * w2) * (f2 * w1)". So, I ended up using additive boost here. > > > > Then we have the combination of the edismax boost, and my custom boost. As > > far as I understand it, when using the boost field with edismax, this > > combination is always performed using multiplicative logic. But the same > > problem exists here as it did with my custom fields. Because if I boost the > > aggregated result of the custom fields using some weight, it doesn't affect > > the order of the documents because that weight influences the edismax boost > > just as much. What I want is to have the weight only influence my custom > > boost value, so that I can control how much (or little) the final score > > should be effected by the custom boost. > > > > So, in both cases I find myself wanting to use the additive boost. But > > surely I must be missing something, right? Am I thinking backwards or > > something? > > > > I don't use any out-of-the-box example indexes, so I can provide you with a > > working URL that shows exactly what I am doing. But in essence my query > > looks like this: > > > > - q=test > > - defType=edismax > > - qf=title^2&qf=mainText1^1 > > - > > totalRanking=div(sum(product(random1,1),product(random2,1.5),product(random3,2),product(random4,2.5),product(random5,3)),5) > > - weightedTotalRanking=product($totalRanking,1.5) > > - bf=$weightedTotalRanking > > - fl=*,score,[explain style=text],$weightedTotalRanking > > > > random1 to random5 are document fields of type double, with random values > > between 0.0 and 1.0. > > > > With this setup, I can change the overall importance of my custom boosting > > using the factor in weightedTotalRanking (1.5 above). But that is only > > because bf is additive. If I switch to the boost parameter, I can no longer > > influence the order of the documents using this factor, no matter how high > > a value I choose. > > > > Am I looking at the this the wrong way? Is there a much better approach to > > achieve what I want? > > > > Regards > > /Jimi >
