1. MediaEval2012 Social Event Detection Task
Event Detection via LDA for the
MediaEval2012 SED Task
Konstantinos N. Vavliakis
Fani A. Tzima
Pericles A. Mitkas
Intelligent Systems and Software Engineering Labgroup
http://issel.ee.auth.gr
Information Technologies Electrical and Computer
Institutes Engineering Department
Centre for Research and Aristotle University of
Technology - Hellas Thessaloniki
Thursday, 4 October 2012

2. MediaEval2012 Social Event Detection Task
Social Event Detection at
MediaEval 2012
 Goal: Discover social events
 3 Challenges:
1. Find technical events in Germany
2. Find all soccer events in Hamburg (Germany)
and Madrid (Spain)
3. Find demonstration and protest events of the
Indignados movement in Madrid
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3. MediaEval2012 Social Event Detection Task
Methodology
Pre- City Topic Identification Event Event
processing Classifier Detection Optimization
Stemming
(Porter
stemmer)
Split
Translate Manually Create Topics Events
(using Google (by location)
Translate)
Clean Text City Identify Select Identify Merge
(remove stop Classifier Topics Relevant Events Events
words/html (tf-idf for (per city, (by detecting (of consecutive
tags) each city) using LDA)
Topics peaks) days)
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4. MediaEval2012 Social Event Detection Task
Preprocessing
 Clean text by removing html tags and stop words
 Translate non-English words
 Perform stemming using the Porter Stemmer
 E.g.:
Title Cleaned Title English Title Stemmed
i-wall wall wall wall
2009...
Pallasso trist // Sad Clown pallasso trist sad clown clown sad sad clown clown sad sad clown
Conjunt Monumental de Sant conjunt monumental set monumental sant pere set monument sant pere
Pere de Terrassa sant pere terrassa terrassa terrassa
Seagull in the port seagull port seagull port seagul port
Winter doesn't affect the small winter doesn affect winter doesn affect small winter doesn affect small
land of the gnomes - 9/365 small land gnomes land gnomes land gnome
Jan-09 january january januari
Tidy chaos - 3/365 tidy chaos tidy chaos tidi chao
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5. MediaEval2012 Social Event Detection Task
City Classification
5 cities
 TF-IDF values of the terms for each city
 Classified photos according to maximum TF-IDF aggregated value
Users:
 Users can not be in more than 2 cities in the same day
 User statistics
Results:
 4149 non classified photos
 Very good results for city classification, excellent at country level
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6. MediaEval2012 Social Event Detection Task
Topic Identification
Manually Create Topics
Photos of a Extract Topics Select Relevant
City using LDA with Gibbs Sampling Topics
Participation
Concept
in Topic
sol 0.1544
spanish 0.1116
revolution 0.1050
acampada 0.0983
puerta 0.0262
mayo 0.0243
manifestación 0.0217
….
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7. MediaEval2012 Social Event Detection Task
Topic Selection
Manually Create Topics
Photos of a Extract Topics Select Relevant
City using LDA with Gibbs Sampling Topics
 Each photos belongs to many topics
 Select photos containing “indignados” or
“acampa” and sum their values per topic
E.g.: PhotoID Topic Participation in Topic Sum
Topic
18 456.58
5776147261 7 0.72 49 223.47
5776147261 14 0.12 0 27.13
5776147261 21 0.08 1 24.17
5776147261 6 0.02 22 23.39
5776147261 25 0.01 ….
….
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8. MediaEval2012 Social Event Detection Task
Event Detection & Optimization
Event Detection
 Find photos of selected topics
 Count photos per day
 If higher than a threshold add them to a new
event
Event Optimization
 Merge events happening in consecutive
days
 Split events by geolocation distance
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9. MediaEval2012 Social Event Detection Task
Results - C1: Technical events in Germany
Precision Recall F-Measure NMI
100 94.9
90
80.98 84.58
80 76.29
0.724
70
63.35
60 0.578
50.98
50
40.52 35.85
40
31.1 25.31
30 26.26
0.16
20
10
0
Selected/Total Selected/Total Selected/Total Manual Manual
Topics: Topics: Topics: Topic Topic
2/50 6/50 8/50
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10. MediaEval2012 Social Event Detection Task
Results – C2: Soccer Events in Hamburg/Madrid
Precision Recall F-Measure NMI 93.49
100 93.49
86.67 91.21 88.18 90.76 88.18 0.847
90 84
81.78 0.85
75.72 77.67 0.768
80
70
60
50
40
30
20
10
0
Selected/Total Selected/Total Selected/Total Manual Manual
Topics: Topics: Topics: Topic Topic
1/50 1/100 1/100
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11. MediaEval2012 Social Event Detection Task
Results – C3: Protest Events of Indignados
Precision Recall F-Measure NMI
100 90.78 90.78
90.76 86.59 85.38 88.91 88.91
90
88.53 89.83
84.29 86.11
80 73.8
70
60
50
40
0.33 0.347
30
20
10
0
Selected/Total Selected/Total Selected/Total Manual Manual
Topics: Topics: Topics: Topic Topic
5/100 5/100 3/50
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12. MediaEval2012 Social Event Detection Task
Conclusions
 Effective and generalized methodology
 The selection of topics is the key
 Topics created by LDA close to manual topic’s results
 Really good precision
 Stemming may improve (slightly) the results
 Problems in “vague” topics
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13. MediaEval2012 Social Event Detection Task
Relevant and Future Work
 Automatically detect all events from a dataset using
detected topics
 Dynamic merging of topics
 The concept of important event
is socially defined -> Personalized detection
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14. MediaEval2012 Social Event Detection Task
Thank You!
Email: kvavliak@issel.ee.auth.gr
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