NAME Lingua::JA::WebIDF - WebIDF calculator SYNOPSIS use Lingua::JA::WebIDF; my $webidf = Lingua::JA::WebIDF->new( api => 'Yahoo', appid => $appid, fetch_df => 1, Furl_HTTP => { timeout => 3 } ); print $webidf->idf("東京"); # low print $webidf->idf("スリジャヤワルダナプラコッテ"); # high DESCRIPTION Lingua::JA::WebIDF calculates WebIDF scores. WebIDF(Inverse Document Frequency) scores represent the rarity of words on the Web. The WebIDF scores of rare words are high. Conversely, the WebIDF scores of common words are low. IDF is based on the intuition that a query term which occurs in many documents is not a good discriminator and should be given less weight than one which occurs in few documents. METHODS new( %config || \%config ) Creates a new Lingua::JA::WebIDF instance. The following configuration is used if you don't set %config. KEY DEFAULT VALUE ----------- --------------- idf_type 1 api 'Yahoo' appid undef driver 'Storable' df_file undef fetch_df 1 expires_in 365 documents 250_0000_0000 Furl_HTTP undef idf_type => 1 || 2 || 3 The type1 is the most commonly cited form of IDF. N idf(t_i) = log ----- (1) n_i N : the number of documents n_i: the number of documents which contain term t_i t_i: term The type2 is a simple version of the RSJ weight. N - n_i + 0.5 w_i = log ---------------- (2) n_i + 0.5 The type3 is a modification of (2). N + 0.5 w_i = log ----------- (3) n_i + 0.5 api => 'Yahoo' || 'YahooPremium' || 'Bing' Uses the specified Web API when fetches WebDF(Document Frequency) scores from the Web. driver => 'Storable' || 'TokyoCabinet' Fetches and saves WebDF scores with the specified driver. df_file => $path Saves WebDF scores to the specified path. If undef is specified, 'yahoo_utf8.st' is used. This file is located in File::ShareDir::dist_dir('Lingua-JA-WebIDF'), and contains the WebDF scores of about 100000 words. There are other format files in the 'share' directory of this library. The 100000 words were fetched from the following data. * Noun.csv and Noun.adjv.csv in IPA dictionary * Japanese WordNet I recommend that you change the file depending on the type of Web API you specifies because WebDF may be different depending on it. fech_df => 0 Doesn't fetch WebDF scores. (If 0 is specified.) If the WebDF score you want to know is already saved, it is used. Otherwise, returns undef. expires_in => $days If 365 is specified, a WebDF score expires in 365 days after fetches it. Furl_HTTP => \%option Sets the options of Furl::HTTP->new. If you want to use proxy server, you have to use this option. idf($word) Calculates the WebIDF score of $word. If the WebDF score of $word is not saved or is expired, fetches it by using the Web API you specified and saves it. df($word) Fetches the WebDF score of $word. If the WebDF score of $word is not saved or is expired, fetches it by using the Web API you specified and saves it. db_open($mode) Opens the database file. If you use TokyoCabinet, you have to open database file by using this method before idf|df|db_close|purge method is called. $mode is 'read' or 'write'. db_close Closes the database file. This method is called automatically when the object is destroyed. So, you might not need to use this method explicitly. purge($expires_in) Purges old data in df_file. If 365 is specified, the data which 365 days elapsed are purged. AUTHOR pawa SEE ALSO Lingua::JA::TFWebIDF Lingua::JA::WebIDF::Driver::TokyoTyrant Bing API: Yahoo API: Tokyo Cabinet: S. Robertson, Understanding inverse document frequency: on theoretical arguments for IDF. Journal of Documentation 60, 503-520, 2004. LICENSE This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.