Hybrid Acquisition of Temporal Scopes for RDF Data

Anisa Rula1, Matteo Palmonari1, Axel-Cyrille Ngonga Ngomo2, Daniel Gerber2, Jens Lehmann2, and Lorenz Bühmann2

1. University of Milano-Bicocca, SITI Lab2. Universität Leipzig, Institut für Informatik, AKSW

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Outline

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1. Introduction & Motivation

2. Approach Overview

3. Details of the Approach

4. Experimental Evaluation

5. Conclusions

team

team

Temporally annotated RDF triples

Alexandre Pato

S.C. Corinthians

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Some facts are always valid while other facts are valid for a certain time interval (volatile facts)

Volatile facts are represented by triples whose validity is defined by a time interval i.e. the temporal scope

Temporal Scoping of RDF triples

2007-2013

2013-2014

Temporal scopes, represented by time intervals

A.C. Milan

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Motivation World changes: relations represented in RDF triples may be valid only

for a specific time interval [Gutierrez et al.,2005]o E.g. <Alexandre_Pato, team, A.C._Milan> [2007,2013]

Many applications have to use temporally annotated RDF tripleso E.g. Temporal Query Answering, Question Answering over KBs, Temporal

Reasoning, Timelines

Challenges Low availability and quality of temporal information in RDF data NLP challenges for web-scale temporal information extraction

(scalability, availability of corpus, conflicting information) [Derczynsk et al., 2013]

Motivation & Challenges

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Temporally annotated RDF triples are largely unavailable or incomplete in the LOD

(Rula et al., 2012)

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Approach Overview: Use the Web as Source of Evidence

Web of Data - RDF (61.9 Billion)

World Wide Web (1.8 Billion)

Source of evidence

Temporally annotated RDF triples

team

teamAlexandre Pato

team

team

Alexandre Pato

S.C. Corinthians

A.C. Milan

2007-2013

2013-2014S.C. Corinthians

A.C. Milan

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Use evidence from the Web for temporal scoping of RDF triples

Web of Documents

Mapping facts to time intervalsTemporal Information Extraction

fact

t1 occ1t2 occ2t3 occ3t4 occ4

Matching Selection

Reasoning

Approach Overview: Hybrid Acquisition of Time Scopes

<s,p,o>

Web of Data

Temporally annotated RDF triples

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Set of disconnected time intervals

<s,p,o>[x1,y1],…,[xn,yn]

Temporal Information Extraction - Web Documents

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DeFacto [Lehmann & al. 2012] Retrieves a set of webpages that

confirm the given RDF triple The RDF triple issued to the search

engine is verbalized by using natural language patterns

Temporal Extension for DeFacto (TempDeFacto) Apply Named Entity Tagger to extract the entities of type Date class Observe the occurrences of the labels of the subject and object in less

than 20 tokens Analyze the context window of n characters before and after subject-

object occurrences in order to retrieve the time points Return a distribution vector of date and their number of occurrences

Temporal Information Extraction - Web Documents

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<Alexandre_Pato,team, A.C._Milan>

“Alexandre Pato” “played for” “A.C. Milan”“Pato” “’s striker” “Milan”“CR7” “Mi”

Pato played for A.C. Milan from 2007 to 2013.A.C. Milan’s top striker Pato left in 2013. In 2013 Pato visited Milan for a short holiday.

2013 17

2007 11

2006 1

…. ….

2010 4

2009 4

1989 2

Occurrences of the labels of the subject and object

Context window of n characters before and after subject-object occurrences

Nam

ed Entity Tagger

DeFacto Vector (dfv)

Temporal Information Extraction - Web of Data

<Alexandre_Pato>

Content negotiation

null null null null null null

0 null null null null null

0 0 null null null null

0 0 0 null null null

0 0 0 0 null null

0 0 0 0 0 null

1989 2000 2006 2007 2008 2013

1989

2000

2006

2007

2008

2013

Relevant Interval Matrix (RIM)

Regular expressions

TAlexandre_Pato= {1989, 2000, 2006, 2007, 2008, 2013}

Relevant Time Points

RDF document dAlexandre_Pato

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The set of time intervals for a given triple with starting and ending time points defined with the set of relevant time points

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null null null null null null

null null null null null

null null null null

null null null

null null

null

1989 2000 2006 2007 2008 2013

1989

2000

2006

2007

2008

2013

1. Matching temporal distribution (dfv) against the relevant time interval matrix

0.004 0.166 0.166 0.736 0.8 2.48

0 0 0.142 1.5 1.555 4.2

0 0 0.002 6 4.666 7.5

0 0 0 0.026 6.5 8.428

0 0 0 0 0.004 8

0 0 0 0 0 0.040

1989 2000 2006 2007 2008 2013

1989

2000

2006

2007

2008

2013

RIM

Mapping Facts to Time Intervals - Matching

MatchingSelection

Reasoning

RDF data

2013 17

2007 11

2006 1

2011 6

2008 2

2016 3

2012 15

2010 4

2009 4

1989 2

𝑠𝑚2007 :2008=11+22 =6.5

Significance Matrix (SM)dfv

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1989 2000 2006 2007 2008 2013

1989

2000

2006

2007

2008

2013

SM

0.004 0.166 0.166 0.736 0.8 2.48

0 0 0.142 1.5 1.555 4.2

0 0 0.002 6 4.666 7.5

0 0 0 0.026 6.5 8.428

0 0 0 0 0.004 8

0 0 0 0 0 0.040

Mapping Facts to Time Intervals - Selection

2. Mapping Selection: top-k function: selects the k intervals that have highest scores in the SM neighbor-x: selects a set of intervals whose significance score is close to

the maximum significance score in the SM matrix, up to a certain threshold x

neighbor-k-x: selects the top-k intervals in the neighborhood of the interval with higher significance score

n eighbor ,𝑥=23

top-k

neighbor-k-x [2007, 2013][2008, 2013]

[2006,2013][2007, 2013][2008, 2013]

[2007,2008][2006,2013][2007, 2013][2008, 2013]

MatchingSelection

Reasoning

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[2007, 2013][2008, 2013]

[ 2007 2013]

Mapping Facts to Time Intervals - Reasoning

3. Interval merging via reasoning based on Allen’s algebra relation

<Alexander_Pato,playsFor, A.C._Milan>

MatchingSelection

Reasoning

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Experimental Setup - Dataset

Dataset # facts Domain Property Equivalent Property

Freebase Yago2DBpedia 1000 Sport team team playsForDBpedia 1000 Politicians office government_positions_held holdsPoliticalPositionDBpedia 500 Celebrities spouse spouse ismarriedTo

Dataset: 2500 DBpedia triples with semantic equivalent triples in Freebase and Yago2

Gold standard: triples annotated with temporal scopes in Yago2 manually curated to correct missing or wrong values

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Experimental Setup - Evaluation Measures

The evaluation measures capture the degree of overlap between the retrieved intervals and the intervals in the gold standard

Precision (for a triple): number of time points in the temporal scope that fall into the time interval in the gold standard

Recall (for a triple): number of time points in the gold standard that are covered by the temporal scope

F1 measure (for a triple): the harmonic mean of precision and recall Macro-averaged F1 (avgF-1): aggregated measure for a set of triples

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2007 2011

2008 2010

2007 2011

2006 2012

2007 2011

2007 2011F1=1F1=0.83F1=0.75

RefR

Temp prop DBpedia Freebase TemporalDeFactoConfig #facts avgF1 Config #facts avgF1 Config #facts avgF1

playsFor top-1 loc 264 0.505 top-1 loc 213 0.477 top-3 311 0.511

holdsPoliticalPosition

neigh-10 702 0.699 neigh-10-2 242 0.549 top-3 709 0.586

ismarriedTo neigh-10 702 0.600 neigh-10 524 0.547 top-3 709 0.545

Good quality of the approach with an avgF1 of up to 70% Using evidence from RDF documents the performance can be

significantly improved (significantly better results for two properties and negligibly worst results for one property)

Experimental Results - Accuracy of Best Configurations for all Properties

Different sources for the creation of the RIM Setup different configurations in the selection and reasoning steps:

o E.g. config top-3 refers to selection function top-3 and reasoning = yes

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Temp prop Source Configuration With reasoning

Without reasoning

#fact avgF1 #fact avgF1playsFor TempDeFacto top-3 311 0.511 505 0.467

holdsPoliticalPosition DBpedia neigh-10 702 0.699 822 0.667

ismarriedTo DBpedia neigh-10 705 0.600 977 0.563

The best results are obtained when reasoning is enabled

Experimental Results - Accuracy with vs. without Reasoning for all Properties

The best configurations for the three properties

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Conclusions & Future Work

Summary Temporal extension of the DeFacto framework Modeling a space of relevant time intervals given an RDF triple Mapping volatile facts to time intervals based on a three-phase algorithm Unsupervised method

Future work Determine when to add or not to add the temporal scope based on the

confidence of the acquisition process Collect additional relevant time points to improve the overall results Show the effectiveness of acquired temporal scopes in temporal query

answering

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Thank you for your attentionQuestion?

#eswc2014Rula

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References

[Rula&2012] Anisa Rula, Matteo Palmonari, Andreas Harth, Steffen Stadtmüller, Andrea Maurino: On the Diversity and Availability of Temporal Information in Linked Open Data. International Semantic Web Conference (1) 2012: 492-507

[Gutiérrez&2005] C. Gutierrez, C. A. Hurtado, and A. A. Vaisman. Temporal RDF. In The 2ndESWC, pages 93-107, 2005

[Lehmann&2012] Jens Lehmann, Daniel Gerber, Mohamed Morsey, Axel-Cyrille Ngonga Ngomo: DeFacto - Deep Fact Validation. International Semantic Web Conference (1) 2012: 312-327

[Ling&2010] X. Ling and D. S. Weld. Temporal information extraction. In 25th AAAI, 2010.

[Derczynsk&2013] L. Derczynski and R. Gaizauskas. Information retrieval for temporal bounding. In 4th ICTIR, pages 29:129–29:130. ACM, 2013.

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