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https://issues.apache.org/jira/browse/NUTCH-25?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12514433
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Doğacan Güney commented on NUTCH-25:
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Doug, thanks for the (very) detailed feedback! This is incredibly helpful.
> I did find a small number of cases where high-ish (>50%) confidence detection
> was wrong:
> http://viniform.typepad.fr/dn/2006/10/mise_jour_du_cl.html
> http://www.buscamaniban.com/fr/patrimoine/coeur-armagnac.php
> http://www.lafite.com/en/html/Corporate/1.html
> http://www.franz-keller.de/8860.html
> http://www.vinesnwines.org/?m=200605
Unfortunately, it seems there is not much we can do about these. I tried adding
a detector.setDeclaredEncoding("UTF-8") before detection and it didn't help
(UTF-8 confidence is surprisingly low, around 25). I also tried jchardet (
http://jchardet.sourceforge.net/ ) with these pages and it doesn't detect them
as UTF-8 either, which is strange considering that mozilla does detect them
correctly.
> Architecturally I think we should store the detected encoding AND the
> confidence in all cases (even when low), instead of storing it only when the
> > confidence meets some threshold. That way the decision of which value to
> use can be made later, in the parser, which can make a "smart"
> decision based upon all the data that's available (detected, sniffed,
> reported, plus confidence value on detection). Then, for example, if there is
> no sniffed or reported value, we could use the detected value, even if the
> confidence is low (especially useful in the TextParser). We could also
> make decisions like "the confidence is medium, but the same value is both
> sniffed and reported, so let's trust that instead," which might fix some > of
> the detection problem cases.
Good idea but implementation-wise I would suggest that we rip out the detection
code from Content.java and move it into parse-html (and whatever else wants to
detect encoding). There will be some code duplication but this way parse-html
can get all the possible matches (via detector.detectAll) and then use sniffed
and reported to make a decision. For example, auto-detect may return
(ISO-8859-1, 60), (UTF-8, 25), sniffed and reported may both be UTF-8. Based on
this data, parse-html can then choose UTF-8 (an idea would be to make sniffed
and reported to add a delta, say 20, confidence). What do you think?
> needs 'character encoding' detector
> -----------------------------------
>
> Key: NUTCH-25
> URL: https://issues.apache.org/jira/browse/NUTCH-25
> Project: Nutch
> Issue Type: New Feature
> Reporter: Stefan Groschupf
> Assignee: Doğacan Güney
> Fix For: 1.0.0
>
> Attachments: NUTCH-25.patch, NUTCH-25_draft.patch
>
>
> transferred from:
> http://sourceforge.net/tracker/index.php?func=detail&aid=995730&group_id=59548&atid=491356
> submitted by:
> Jungshik Shin
> this is a follow-up to bug 993380 (figure out 'charset'
> from the meta tag).
> Although we can cover a lot of ground using the 'C-T'
> header field in in the HTTP header and the
> corresponding meta tag in html documents (and in case
> of XML, we have to use a similar but a different
> 'parsing'), in the wild, there are a lot of documents
> without any information about the character encoding
> used. Browsers like Mozilla and search engines like
> Google use character encoding detectors to deal with
> these 'unlabelled' documents.
> Mozilla's character encoding detector is GPL/MPL'd and
> we might be able to port it to Java. Unfortunately,
> it's not fool-proof. However, along with some other
> heuristic used by Mozilla and elsewhere, it'll be
> possible to achieve a high rate of the detection.
> The following page has links to some other related pages.
> http://trainedmonkey.com/week/2004/26
> In addition to the character encoding detection, we
> also need to detect the language of a document, which
> is even harder and should be a separate bug (although
> it's related).
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