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Document Summarization
Elias Haileselassie
Martha Teffera
May 14, 2011
School of Information Science
Addis Ababa University
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Outline
What is Summarization
Input & Output
Examples
Types of Summaries
Single document vs multi document
Extract vs Abstract
Generic vs Query Oriented Functions
Indicative
Informative
Summarization Techniques Sentence Extraction
Evaluating Summaries
Applications
Pros and Cons
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What is Summarization?
Summarization is the creation of ashortened version of a documenteither manually or automatically
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What is Summarization? …cnt’d
Automatic Document Summarization is the
creation of a shortened version (summary) of adocument by a computer program with outlosing content
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Input & Output
A summary input can be in the form of apicture, a movie, an audio segmentor a text document
The output to be summarized may be inthese different multimedia forms.
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Input & Output …cnt’d
Input
Text
Compression Rate or Summary Length
rate = Summary Length/Source Length
Output
Summary Text/Audio
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Examples of Summaries Newspaper headlines
A preview of a video show
Abstracts of scientific articles Reviews of books and movies
A library catalog of abstracts of articles
A table of contents for a book ,magazine or any kind of document
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Types of summarization
Depending on the input
Single document summaries Multi document summaries
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Types of summarization …cnt’d
Depending on the output(process)Extract summaries
Abstract summaries
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An extract is a summary consisting entirely of materialcopied from the input.
It is a custom to speak of an extract of K%condensation: so K% of the input's words/sentences/paragraphs may appear in theextract.
Extract Summaries
Types of summarization …cnt’d
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In contrast, an abstract is a summary at least some of whose material is not present in the input
In general, abstracts offer the possibility of higherdegrees of condensation: a short abstract may offermore information than a longer extract.
Abstract Summaries
Types of summarization …cnt’d
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Generic vs Query-OrientedDepending on the purpose, a summary can be
Generic - reflect the author's point of view withrespect to all important topics in the input text
Query Oriented (user-focused ) - reflect only the topics
in the input text that are specific to a given query
Types of summarization …cnt’d
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Indicating what is inside a document
helping the user to decide whether to read theinformation source, or not
Replace the original document with out losing content
Saves time
Functions of summarization
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Indicative summaries An indicative summary can provide only an indication
of the main topics in the input text
Thus, an indicative abstract is aimed at helping theuser to decide whether to read the informationsource, or not
The main purpose is to suggest the contents of the
document without giving away detail on thedocument’s content.
Functions of summarization
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Informative summaries
An informative summary is meant to represent (and
often replace) the original document. It should contain all the pertinent information
necessary to convey the core information and omitunnecessary information
Functions of summarization …cnt’d
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An ideal method
1. Understanding the text
2. Transforming the analytical result of the text into arepresentation(model) of a summary
3. Generating a summary from the internal
representation
Summarization Techniques
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Current methods
1. Extracting the important parts (sentences) in the text
2. Just arranging them in the order in the text
Summarization Techniques cnt’d
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Sentence Extraction
Word frequency in text
Title of text Position of sentence
Cue phrases in text
Summarization Techniques cnt’d
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Ideal evaluation
Measure the information content
Compression Ratio: CR = (length S) / (length doc)
Retention Ratio: RR = (info in S) / (info in T)
Evaluating Summaries
l
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Practical evaluation
Comparing with existing summaries for similarity word overlap
Measure Recall & Precision -> 2PR/(P+R)
Evaluating Summaries …cnt’d
Relevant Non Relevant
System Relevant A B
System Non-Relev. C D
B A
A P
+
=:Precision
C A
A R
+
=:Recall
Applications
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ApplicationsSearch Engines: Result Summarization
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Applications …cnt’d
shablast.com
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Applications …cnt’d
Table of Contents Generation - MS Word
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Applications …cnt’d
News Headline/Summary Generation
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Applications …cnt’d
Book/Article Summarization - Copernic Summarizer
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Pros and Cons
ProsSaves time
Helps decision making/to read or
not to readHelps select the right
document(information overload)
Cons
Slows search engine result display
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Thank you!
