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Open Text summarizer
---------------------
Nadav Rotem 2003
nadav256@hotmail.com
---------------------
The open text summarizer is an open source tool for summarizing texts. The program
reads a text and decides which sentences are important and which are not. OTS will
create a short summary or will highlight the main ideas in the text.
OTS is both a library and a command line tool. Word processors such as AbiWord
and KWord can link to the library and summarize documents while the command line tool
lets you summarize text on the console. The program can either print the summarized
text as text or HTML. If in HTML, the important sentences are highlighted.
The program is multi lingual and works with UTF-8 encoding.
Supported languages:
(ca,bg,cs,cy,da,de,el,en,eo,es,et,eu,fi,fr,ga,gl,he,hu,ia,id,is,it,lv,mi,ms,mt,nl,nn,
pl,pt,ro,ru,sv,tl,tr,uk,yi)
Basque (seminal)
Bulgarian (seminal)
Catalan (seminal)
Czech (seminal)
Danish (seminal)
Dutch
English
Esperanto (seminal)
Estonian (seminal)
Finnish (seminal)
French (seminal)
Galician (seminal)
German (seminal)
Greek (seminal)
Hebrew
Hungarian (seminal)
Icelandic (seminal)
Indonesian (seminal)
Interlingua (seminal)
Irish (Gaelic) (seminal)
Italian (seminal)
Latvian (seminal)
Malaysian (seminal)
Maltese (seminal)
Maori (seminal)
Norwegian Nynorsk (seminal)
Polish (seminal)
Portuguese (seminal)
Romanian (seminal)
Russian (seminal)
Spanish (seminal)
Swedish (seminal)
Tagalog (Pilipino) (seminal)
Turkish (seminal)
Ukrainian (seminal)
Welsh (seminal)
Yiddish (seminal)
Command line Usage:
$ ots
--ratio [0..100] :select the summary ratio
--html :print summary in highlighted html form
--keywords :print key words in the article
--dic :use dictionary other then english, for example 'he' or 'es'
--about :tells that the article talks about
--file :input file
--out :output file
--help :print this help screen
example1:
ots articles/sacbee1.txt --ratio 20 --html
This command will summarize the article from the Sacramento Bee and highlight the 20% of
sentences most important to the content of the article.
example2:
ots --ratio 40 --file big_article.txt
This command will summarize the article down to 40% and print it.
How it works:
The Idea behind OTS is that the important ideas in an article are described with
many of the same words while redundant information uses less technical terms
and is not related to the main subject of the article. Important lines are lines
that are related to the subject of the article. The subject of the article is the
list of ideas that are most discussed in the article.
In practice , the article is scanned once and a list of all of the words and their
occurrence in the text is stored in a list. After sorting this list by the
occurrence of words in the text we will see a list similar to this:
11 are
17 is
16 a
14 Harry
14 on
13 Sally
11 Love
11 such
4 an
2 taxi
1 university
1 chicago
1 meets
...
...
Now we will remove all the words that are common in the English language using a
dictionary file. Example of such words: "The","a","since","after","will".
These words are words that don't teach us anything about the subject of the article.
Knowing that the word "Police" is in a given text can tell us that the article might
talk about the police , however knowing that the word "will" is in the text can't
teach us anything about the subject of the text.
After removing the redundant words the new list will look like this:
14 Harry
13 Sally
11 Love
2 taxi
1 university
1 chicago
1 meets
From this list we may assume that the text talks about "Harry , Sally , Love".
So an important sentence in the text will be a sentence that talks about Harry,
Sally and Love. A sentence that talks about the university of Chicago may be
neglected because we find the word "chicago" only once in the text, so we may assume
that "chicago" is not one of the main ideas in the text. Each sentence is given
a grade based on the the keywords in it. A line that holds many important words will
be given a high grade. To produce a 20% summary we print the top 20% sentences with
the highest grade.
Ots will not work on books because they cover too many topics. however, each
page may be fed individually, this will produce a good result. Poems or other
non-standard texts will not produce a good result because they are structured
in a "funny" way.
Every new language to be implemented needs to contain a list of VERY common words
in the language. 250 words is more than enough. See en.dic for example. Writing such
a dictionary is an iteratice process. It is suggested that the author of such a
dictionary will try to scan a few articles using OTS and try it with the "--keywords"
flag on. This will tell him if OTS thinks for some reason that "his" is the subject
of the text. If this is the case then "his" needs to be added to the dictionary.
Stemming:
stemming is the ability to take a word such as "running" and trace it back to its
original form to the word "run". We use this feature to group together all of the
the derivatives of a certain words. Now what we group together these words
ots will know what the subject of this article is the one word "run" and not
("running","run", "runnable" ...). Now, when we encounter a sentence that talks
about some "runner" we will know to that it is related to the topic of the article.
In previous versions this has never been done because "running"!="run";
The stemming support is now integrated into OTS. To allow stemming I had to create a new
file format that will hold the stemming rules. That format is XML based. libxml2 is being used.
Example:
[dam]==[dams] stem[dam]
[asking]==[asked] stem[ask]
[build]==[building] stem[build]
[accidents]==[accident] stem[accident]
[policing]==[police] stem[polic]
[reported]==[report] stem[report]
[years]==[year] stem[year]
[increased]==[increase] stem[increas]
[study]==[studies] stem[study]
[reported]==[reports] stem[report]
[gates]==[gate] stem[gat]
[locked]==[lock] stem[lock]
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