Going beyond its role as an encyclopedia, Wikipedia becomes a global memory place for high-impact events, such as, natural disasters and manmade incidents, thus influencing collective memory, i.e., the way we remember the past. Due to the importance of collective memory for framing the assessment of new situations, our actions and value systems, its open construction and negotiation in Wikipedia is an important new cultural and societal phenomenon. The analysis of this phenomenon does not only promise new insights in collective memory. It is also an important foundation for technology, which more effectively complements the processes of human forgetting and remembering and better enables us to learn from the past. In this paper, we analyse the long-term dynamics of Wikipedia as a global memory place for high-impact events. This complements existing work in analysing the collective memory negotiation and construction process in Wikipedia directly following the event. In more detail, we are interested in catalysts for reviving memories, i.e., in the fuel that keeps memories of past events alive, interrupting the general trend for fast forgetting. For this purpose, we study the trigger of revisiting behavior for a large set of event pages by exploiting page views and time series analysis, as well as identify of most important catalyst features.

1. “Concise Preservation by Combining Managed Forgetting
and Contextualized Remembering”
EU/FP7 ForgetIT Project (2013-2016)
http://www.forgetit-project.eu
What Triggers Human Remembering of Events?
Large-Scale Analysis of Collective Memory in Wikipedia
Nattiya Kanhabua, Tu Ngoc Nguyen and Claudia Niederée
L3S Research Center , Hannover, Germany

2. Motivation: ForgetIT Project
Human Forgetting and Remembering
Collective Memory in Wikipedia
Experiments and Discussion
Conclusions
Outline

3. However, we are facing:
• Dramatic increase in content creation (e.g. digital photos)
• Increasing use of mobile devices with restricted capacity
• Information overload and changing professional and private lives
• Inadvertent forgetting due to lack of systematic preservation
Forgetting plays a crucial role for human remembering and life
(focus on current, relevant information; ignore redundant details)
Managed forgetting ≠ automatic deletion
Instead: a range of forgetting options e.g.
• Resource condensation
• Change of indexing & ranking
• Reduction of redundancy
A computer that forgets intentionally ?
And, in context of digital preservation??

4. However, we are facing:
• Dramatic increase in content creation (e.g. digital photos)
• Increasing use of mobile devices with restricted capacity
• Information overload and changing professional and private lives
• Inadvertent forgetting due to lack of systematic preservation
Forgetting plays a crucial role for human remembering and life
(focus on current, relevant information; ignore redundant details)
Managed forgetting ≠ automatic deletion
Instead: a range of forgetting options e.g.
• Resource condensation
• Change of indexing & ranking
• Reduction of redundancy
A computer that forgets intentionally ?
And, in context of digital preservation??
Managed forgetting = to remember the right information

5. Individual memories are subject to a fast
forgetting process [Ebbinghaus, 1885]
• Rapidly forget details -> “less redundancy”
Episodic memory (of one’s past event) is
reconstructed from similar events/context
• Rely on common patterns -> “false memory”
Memory bumps in the forgetting curve is
caused by reminding or triggering of:
• A physical object (e.g. a printed photo)
• A digital memory system
• Different subsequent events
Human Forgetting and Remembering
H. Ebbinghaus, Über das Gedächtnis. Untersuchungen zur experimentellen Psychologie. Duncker & Humblot,
Leipzig, 1885.
E. Tulving, Episodic memory: From mind to brain. Annual review of psychology, vol. 53, no. 1, pp. 1-25, 2002.

6. “ Collective memory is a socially constructed, common image (memory)
of the past of a community, which frames its current understanding
and actions.” [Halbwachs, 1950]
• Crowd phenomenon and important to societal processes
• Not static as determined by the concerns of the present
From Individual Memories to Collective Memory
M. Halbwachs, On collective memory. Chicago: The University of Chicago Press, 1950 (Translation).
Flashbulb memories in cognitive psychology
• A study of remembering of high-impact events, e.g.,
The British Royal Wedding or September 11 attacks
• Aspects: details, confidence, consistency of memory
over time, impact of media coverage
• Qualitative study: limited number of events and users

7. Collective Memory in Wikipedia
Wikipedia as a source for global memory
• Largest and most up-to-date online encyclopedia
(19M registered users, 30K active editors)
• Social negotiation and construction reflected in
early editing activities and talk pages
• Indicators for identifying real-world events
C. Pentzold, The online encyclopaedia wikipedia as a global memory place, Memory Studies, 2009.
M. Georgescu, N. Kanhabua, D. Krause, W. Nejdl, and S. Siersdorfer, Extracting event-related information
from article updates in wikipedia, ECIR'2013.
View logs as the signal for collective memory
• Public page view traffics with a long time span
• Not directly reflect how people forget; significant
patterns are a good estimate public remembering
• Large-scale analysis complements (1) qualitative
studies (2) analyzing article content (scalability)

8. Contributions
First study of identifying catalysts for event memory triggering by using
time series analysis techniques:
• temporal correlations in peaking page visits between events,
• a surprise score or the residual sum of squares on prediction error, and
• the skewness of view shapes as a catalyst for memories
Identify the relationship between events by using different features
• the role of time passed, the same types of events, the size or magnitude of
events, the near-by city or neighbor country
Analyze over 5500 high-impact events from 11 event categories
Related to the previous study by [Au Yeung and Jatowt, 2011]
• Analyzed references to the past (as an indicator to what is remembered) in a
large news collection for identifying, which years are most frequently referenced
C.-m. Au Yeung and A. Jatowt, Studying how the past is remembered: Towards computational history
through large scale text mining, CIKM’2011

9. We propose a 3-step approach, for a given event:
1. Compute “remembering scores” of past events within the same category
2. Rank related past events by the computed remembering scores
3. Identify features (e.g., time, location) having a high correlation with remembering
Our Approach

10. Remembering scores: a linear
combination of three features:
1. Cross-correlation coefficient (CCF)
2. Sum of squared error (SSE)
3. Skewness (Kurtosis)
Measuring Signals for Memory Revival

11. Remembering scores: a linear
combination of three features:
1. Cross-correlation coefficient (CCF)
2. Sum of squared error (SSE)
3. Skewness (Kurtosis)
Measuring Signals for Memory Revival

12. Remembering scores: a linear
combination of three features:
1. Cross-correlation coefficient (CCF)
2. Sum of squared error (SSE)
3. Skewness (Kurtosis)
Measuring Signals for Memory Revival
Remembering = α•CCF + β•SSE + γ•Kurtosis

13. Features for Triggered Remembering
Temporal similarity:
• Time distance between two events (in days, months or years)
• Time distance based on exponential decay functions
Location similarity:
• Map a geographic hierarchy of event locations as follows
 city -> state -> country -> neighbor countries -> continent
• Assign 4 scale values: 4 to same city, 3 to state, 2 to country,1 to continent
Impact of Events:
• Damaged area/properties/cost/fatalities
• Magnitude (for earthquake events)
• Highest winds, lowest pressure (for Atlantic hurricanes)
N. Kanhabua and K. Nørvåg: Determining time of queries for re-ranking search results. ECDL 2010
J. Strötgen, M. Gertz, and C. Junghans: An event-centric model for multilingual document similarity. SIGIR 2011

14. Experiments
Datasets:
• Page views statistics 2007-2013
• A large set of 5,500 events
• From 11 event-related categories
• α = 0.5, β = 0.4, γ = 0.1

15. Temporal and spatial distributions
• Strong focus on more recent events
• Better coverage with increasing popularity
• Most frequent locations depending on event types
Temporal and Spatial Distributions

16. Temporal and spatial distributions
• Strong focus on more recent events
• Better coverage with increasing popularity
• Most frequent locations depending on event types
Temporal and Spatial Distributions

17. Temporal and spatial distributions
• Strong focus on more recent events
• Better coverage with increasing popularity
• Most frequent locations depending on event types
Temporal and Spatial Distributions

18. Category: Atlantic Hurricane
Distributions of remembering scores
• Hurricane Sandy (Form date: October 22, 2012, Affected area: Mid-Atlantic)
• Hurricane Hanna (Form date: August 28, 2008, Affected area: US east coast)

19. Category: Atlantic Hurricane
Distributions of remembering scores
• Hurricane Sandy (Form date: October 22, 2012, Affected area: Mid-Atlantic)
• Hurricane Hanna (Form date: August 28, 2008, Affected area: US east coast)
Location and time have a low effect on
remembering scores for this category.

20. Category: Atlantic Hurricane
Top-10 events triggered by the two events
• Hurricane Hanna commemorates Hurricane Gustav, the freshest hurricane
stuck at the area of Puerto Rico and East Coast
• Hurricane Sandy triggers 1991 Perfect Storm initially formed around Canada
area, which t is high impact and most destructive

21. Category: Atlantic Hurricane
Top-10 events triggered by the two events
• Hurricane Hanna commemorates Hurricane Gustav, the freshest hurricane
stuck at the area of Puerto Rico and East Coast
• Hurricane Sandy triggers 1991 Perfect Storm initially formed around Canada
area, which t is high impact and most destructive

22. Category: Aviation accidents
Mixture of impact factors, such as, time and location
• Qantas Flight 32 (crashed on 4 November 2010) triggers remembering of
(1) Qantas Flight 30 and British Airways Flight 9 (both going to Australia),
and (2) Aero Caribbean Flight 883 (most recent event)
Most recent

23. Category: Aviation accidents
Mixture of impact factors, such as, time and location
• Qantas Flight 32 (crashed on 4 November 2010) triggers remembering of
(1) Qantas Flight 30 and British Airways Flight 9 (both going to Australia),
and (2) Aero Caribbean Flight 883 (most recent event)
Same
destination

24. Category: Aviation accidents
Mixture of impact factors, such as, time and location
• Qantas Flight 32 (crashed on 4 November 2010) triggers remembering of
(1) Qantas Flight 30 and British Airways Flight 9 (both going to Australia),
and (2) Aero Caribbean Flight 883 (most recent event)
Same
destination
Deadliest (two
aircraft collided)
Concorde

25. Category: Earthquakes
A series of earthquake events at Christchurch, New Zealand
• 2010 Canterbury earthquake triggers 2010 Haiti earthquake (recent and high-
impact) and two close-by events, and high-impact historical earthquakes
• 2011 Christchurch earthquake shows locality focus, i.e., people seem to be
interested in the previous events in the same region
• June 2011 Christchurch earthquake, the remembered events are dominated
by the two predecessor events

26. Category: Earthquakes
A series of earthquake events at Christchurch, New Zealand
• 2010 Canterbury earthquake triggers 2010 Haiti earthquake (recent and high-
impact) and two close-by events, and high-impact historical earthquakes
• 2011 Christchurch earthquake shows locality focus, i.e., people seem to be
interested in the previous events in the same region
• June 2011 Christchurch earthquake, the remembered events are dominated
by the two predecessor events

27. Category: Earthquakes
A series of earthquake events at Christchurch, New Zealand
• 2010 Canterbury earthquake triggers 2010 Haiti earthquake (recent and high-
impact) and two close-by events, and high-impact historical earthquakes
• 2011 Christchurch earthquake shows locality focus, i.e., people seem to be
interested in the previous events in the same region
• June 2011 Christchurch earthquake, the remembered events are dominated
by the two predecessor events

28. Category: Earthquakes
A series of earthquake events at Christchurch, New Zealand
• 2010 Canterbury earthquake triggers 2010 Haiti earthquake (recent and high-
impact) and two close-by events, and high-impact historical earthquakes
• 2011 Christchurch earthquake shows locality focus, i.e., people seem to be
interested in the previous events in the same region
• June 2011 Christchurch earthquake, the remembered events are dominated
by the two predecessor events
Look beyond single events, especially, if there are
several events in temporal and local proximity.

29. Category: Earthquakes
A series of earthquake events at Christchurch, New Zealand
• 2010 Canterbury earthquake triggers 2010 Haiti earthquake (recent and high-
impact) and two close-by events, and high-impact historical earthquakes
• 2011 Christchurch earthquake shows locality focus, i.e., people seem to be
interested in the previous events in the same region
• June 2011 Christchurch earthquake, the remembered events are dominated
by the two predecessor events
Look beyond single events, especially, if there are
several events in temporal and local proximity.

30. Category: Terrorist incidents
Interesting observation: semantic similarity between events
• June 2012 Kaduna church bombings triggers other religion terror attacks
• 2008 Mumbai attacks trigger terror attacks in business, entertainment and hotels
2nd
5th
24th

31. Category: Terrorist incidents
Interesting observation: semantic similarity between events
• June 2012 Kaduna church bombings triggers other religion terror attacks
• 2008 Mumbai attacks trigger terror attacks in business, entertainment and hotels
2nd
7th
15th

32. Conclusions
We identified some first pattern for event memory triggering for diverse
event types including natural and manmade disasters as well as
accidents and terrorism.
Our analysis confirmed the influence of closeness in time and location,
but the semantic similarity of events also influences which event
memories are triggered by an event.
In our future work, we plan to deepen our systematic analysis of factors
for revisiting past events and of the combination of those factors.
We also plan to investigate external factors such as media coverage
linking new events to past events or reflection of such relationships in
other types of social media.

33. What do you remember?
Thanks for your attention!