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https://issues.apache.org/jira/browse/TIKA-496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901977#action_12901977
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Ken Krugler commented on TIKA-496:
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I think that the current profile data was generating from a corpus of the same
set of documents (EU publications) translated into the target languages. In
that situation, the total ngram counts should be similar, so the problem you
mention doesn't appear.
I'd be in favor of changing the profile file format to have explicit
frequencies versus counts.
> Language identifier profile comparison favors large profiles
> ------------------------------------------------------------
>
> Key: TIKA-496
> URL: https://issues.apache.org/jira/browse/TIKA-496
> Project: Tika
> Issue Type: Bug
> Components: languageidentifier
> Affects Versions: 0.7
> Reporter: Jan Høydahl
>
> I think I've found a flaw in the distance algorithm.
> In LanguageProfile.java distance() method, we normalize the frequency for an
> ngram by dividing by the total count.
> The total count for a profile is simply the sum of all counts in the profile.
> Problem is, that the .ngp files are cutoff at 1000 entries, and the total
> count is then the sum of all those 1000 entries.
> However, there will be a long-tail of lower frequency ngrams which are cut
> off and therefore not included in the total count.
> Effect is that the ngrams from profiles with large training set are more
> important than ngrams from smaller training set.
> You can see this effect especially well when classifying short texts in a
> language wich has similar sister languages with larger training sets. My
> example is "no" vs "da".
> Sample from the tail of "no.ngp":
> _gå 461
> ask 461
> ria 459
> små 459
> ...and from the tail of "dk.ngp":
> dbr 966
> ost 966
> ævn 964
> It is obvious that "dk" has a longer tail after cutoff than "no" and
> therefore a larger sum.
> A solution is to count the real total count when generating the .ngp file and
> storing the total in the profile file itself, instead of counting when
> loading the cutoff profile.
> Alterniatvely, normalize counts before writing the .ngp file, so that the top
> entry is always 100000
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