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Event Clusters Detection on Flickr Images using a Suffix-Tree Structure

This document proposes an approach to detect event clusters from Flickr images using a suffix-tree structure. It discusses challenges in event detection from large, noisy, and weakly annotated photo collections from social media sites. Prior works on event clustering from images focused on visual/temporal data from individual users and were not scalable. Other approaches used temporal data from tags but did not consider location information or scale to large datasets. The proposed approach aims to address these limitations by clustering events based on spatial, temporal and contextual information from Flickr images using a suffix-tree data structure.

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1 Event Cluster Detection on Flickr Images using a Suffix-Tree Structure Massimiliano Ruocco and Heri Ramampiaro Dept. Of Computer and Information Science Norwegian University of Science and Technology ruocco@idi.ntnu.no Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
2 Outline Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
3 Outline 1.  Introduction 1.  Problem Statement 2.  Related Works 3.  Contributions 2.  Proposed approach 1.  Problem definition 2.  Preliminary 3.  Algorithm Overview 3.  Evaluation 4.  Conclusions Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
4 Problem Statement Event Detection Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
5 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
6 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): -  Objective: aggregate stories over time into single event topic (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
7 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): -  Objective: aggregate stories over time into single event topic Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
8 Problem Statement Event Detection Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
9 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
10 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: -  Retrospective Detection : discover unidentified events in a collection of news [Yang et al. 1998] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
11 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: -  Retrospective Detection : discover unidentified events in a collection of news [Yang et al. 1998] -  Online Detection : detect events in real-time from a stream of news [Brants et al. 2003] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
12 Problem Statement Web Photo-Sharing Apps – New Needs Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
13 Problem Statement Web Photo-Sharing Apps – New Needs Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
14 Problem Statement Web Photo-Sharing Apps – New Needs Time! 26 Oct 2010 User! RMax Location! 26:12, 23:14 Tags! Roma, Sky, Bridge …! Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
15 Problem Statement Web Photo-Sharing Apps – New Needs Retrieve New Needs Browse Time! 26 Oct 2010 User! RMax Location! 26:12, 23:14 Knowledge Extraction Tags! Roma, Sky, Bridge …! Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
16 Problem Statement Challenges Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
17 Problem Statement Challenges -  Event detection on Tagged Picture from Photo-Sharing Apps -  Web-scale environment -  Use of contextual information -  Noisy annotation Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
18 Problem Statement Challenges -  Event detection on Tagged Picture from Photo-Sharing Apps -  Web-scale environment -  Use of contextual information -  Noisy annotation Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
19 Related Works Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
20 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
21 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! -  Event/Place Semantic Identification (Temporal information) [Rattenbury et al. 2007] -  Extraction of event and place semantics for tags assigned to Flickr photos -  Scale-Structure Identification (SSI) method to analyze the tag usage distribution -  SSI is limited for large dataset! -  Location information is not considered! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
22 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! -  Event/Place Semantic Identification (Temporal information) [Rattenbury et al. 2007] -  Extraction of event and place semantics for tags assigned to Flickr photos -  Scale-Structure Identification (SSI) method to analyze the tag usage distribution -  SSI is limited for large dataset! -  Location information is not considered! -  Event Tag Detection (Spatial/Temporal information) [Chen, Roy 2009] -  Detect event tags from Flickr photos -  As [Rattenbury et al. 2007] use SSI method to analyze the tag usage distribution -  SSI is used over locational and spatial distributions simultaneously Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
23 Problem Definition Hypothesis Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
24 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
25 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
26 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Event Cluster ej  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
27 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Event Cluster ej  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Not the opposite  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
28 Problem Definition Hypothesis – Landmark clusters Location Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
29 Problem Definition Hypothesis – Landmark clusters Location Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
30 Problem Definition Hypothesis – Landmark clusters Landmark Location Clusters Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Not the opposite  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
31 Problem Definition Hypothesis – Event clusters Location g time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
32 Problem Definition Hypothesis – Event clusters Location g dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
33 Problem Definition Hypothesis – Event clusters Location g applepies! dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
34 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
35 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } The opposite is true  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
36 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } The opposite is true  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
37 Problem Definition New Formulation Event Event Cluster ek Clusters Location Sdgt Location Sgt = g applepies! g applepies! dt time time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
38 Problem Definition New Formulation Event Event Cluster ek Clusters { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) Location Sdgt € Location Sgt = g applepies! g applepies! dt time time Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
39 Preliminary Suffix-Tree Clustering [Zamir 1998] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
40 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
41 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
42 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
43 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
44 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
45 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
46 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model -  Snippet-tolerant Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
47 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model -  Snippet-tolerant -  Overlapped clusters Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
48 Preliminary Suffix-Tree Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
49 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
50 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Papua ‘apua’ ‘pua’ ‘ua’ ‘a’ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
51 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Papua ‘apua’ ‘pua’ ‘ua’ ‘a’ -  Suffix-Tree construction performs in linear time (O(n)) ([Ukkonen 1995]) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
52 Algorithm Overview Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
53 Algorithm Overview Data cleaning Data extension Suffix Tree Construction Ii = (T, g, dt) Event clusters extraction Event Clusters merge … Primary! Party! Election! Campaign! … Concert! Music! John! … … Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
54 Algorithm Overview Data Cleaning and Extension Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
55 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
56 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
57 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] where s1 and s2 encoding function from date/location to string Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
58 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
59 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string acmm2010 26Oct2010 43.77:11.24 acmm2010 florence 26Oct2010 43.77:11.24 florence multimedia 26Oct2010 43.77:11.24 multimedia Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
60 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string acmm2010 26Oct2010 43.77:11.24 acmm2010 T’ florence T’’ 26Oct2010 43.77:11.24 florence multimedia 26Oct2010 43.77:11.24 multimedia s1(26/10/2010) s2(43.777864,11.249029) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
61 Algorithm Overview ST Construction and Event Extraction Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
62 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
63 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
64 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
65 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
66 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
67 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l -  IF (Ψl = Ψ’l)  Ψl ([s1(dt) + s2(g) + ti ]) is event cluster € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
68 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l -  IF (Ψl = Ψ’l)  Ψl ([s1(dt) + s2(g) + ti ]) is event cluster € -  Label inferred from the structure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
69 Algorithm Overview Extraction and Merge Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
70 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
71 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} -  Merge semantically similar cluster: Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
72 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} -  Merge semantically similar cluster: ei ∩ e j Ψ’l θ (ei ,e j ) = min(ei ,e j ) Ψl € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
73 Evaluation - Dataset Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
74 Evaluation - Dataset -  Dataset collected from Flickr -  Only geo-tagged picture -  12 June 2008 – 11 June 2010 (729 days) -  San Francisco Area #Images ~ 350K #Tags ~ 3M Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
75 Evaluation - Measure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
76 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
77 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
78 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
79 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Rk Rk : relevant clusters in the Top-K Precision : first k returned K € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
80 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Rk Rk : relevant clusters in the Top-K Precision : first k returned K Top-20 (K=20) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
81 Evaluation -  Experiment on different granularity in time and space -  Time: 1 day 1 week Example 2008Oct12 2008:43 -  Space: Latitude Precision Longitude Square Size Precision (Meters) 0.01 0.01 1000m X 1000m 0.005 0.005 500m X 500m 0.002 0.002 200m X 200m 0.001 0.001 100m X 100m Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
82 Evaluation - Results 100 m 200 m 500 m 1000 m 1 Day 1 Week 1 Day 1 Week 1 Day 1 Week 1 Day 1 Week #Clusters #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. 1 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 2 2 100% 2 100% 2 100% 2 100% 2 100% 2 100% 2 100% 1 50% 3 3 100% 3 100% 3 100% 3 100% 3 100% 3 100% 3 100% 2 67% … 20 15 75% 14 70% 15 75% 14 70% 14 70% 13 65% 13 65% 14 70% Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
83 Evaluation - Results Top-20 precision Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
84 Conclusion Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
85 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
86 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
87 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
88 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
89 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
90 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal -  Spatial and Time information considered Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
91 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal -  Spatial and Time information considered -  Analysis of different granularity of time and space Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
92 Thanks ( ) for the attention! http://www.idi.ntnu.no/~ruocco/ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
93 Thanks ( ) for the attention! QUESTIONS? http://www.idi.ntnu.no/~ruocco/ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010

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Event Clusters Detection on Flickr Images using a Suffix-Tree Structure

  • 1.
    1 Event Cluster Detection on Flickr Images using a Suffix-Tree Structure Massimiliano Ruocco and Heri Ramampiaro Dept. Of Computer and Information Science Norwegian University of Science and Technology ruocco@idi.ntnu.no Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 2.
    2 Outline Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 3.
    3 Outline 1.  Introduction 1.  Problem Statement 2.  Related Works 3.  Contributions 2.  Proposed approach 1.  Problem definition 2.  Preliminary 3.  Algorithm Overview 3.  Evaluation 4.  Conclusions Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 4.
    4 Problem Statement Event Detection Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 5.
    5 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 6.
    6 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): -  Objective: aggregate stories over time into single event topic (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 7.
    7 Problem Statement Event Detection -  Event detection topic has its origin from the TDT (Topic Detection and Tracking) project(1): -  Objective: aggregate stories over time into single event topic Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] (1) http://projects.ldc.upenn.edu/TDT/! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 8.
    8 Problem Statement Event Detection Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 9.
    9 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 10.
    10 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: -  Retrospective Detection : discover unidentified events in a collection of news [Yang et al. 1998] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 11.
    11 Problem Statement Event Detection -  Most previous works focus on time-tagged document streams can be classified as: -  Retrospective Detection : discover unidentified events in a collection of news [Yang et al. 1998] -  Online Detection : detect events in real-time from a stream of news [Brants et al. 2003] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 12.
    12 Problem Statement Web Photo-Sharing Apps – New Needs Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 13.
    13 Problem Statement Web Photo-Sharing Apps – New Needs Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 14.
    14 Problem Statement Web Photo-Sharing Apps – New Needs Time! 26 Oct 2010 User! RMax Location! 26:12, 23:14 Tags! Roma, Sky, Bridge …! Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 15.
    15 Problem Statement Web Photo-Sharing Apps – New Needs Retrieve New Needs Browse Time! 26 Oct 2010 User! RMax Location! 26:12, 23:14 Knowledge Extraction Tags! Roma, Sky, Bridge …! Huge Amount of Pictures Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 16.
    16 Problem Statement Challenges Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 17.
    17 Problem Statement Challenges -  Event detection on Tagged Picture from Photo-Sharing Apps -  Web-scale environment -  Use of contextual information -  Noisy annotation Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 18.
    18 Problem Statement Challenges -  Event detection on Tagged Picture from Photo-Sharing Apps -  Web-scale environment -  Use of contextual information -  Noisy annotation Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 19.
    19 Related Works Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 20.
    20 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 21.
    21 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! -  Event/Place Semantic Identification (Temporal information) [Rattenbury et al. 2007] -  Extraction of event and place semantics for tags assigned to Flickr photos -  Scale-Structure Identification (SSI) method to analyze the tag usage distribution -  SSI is limited for large dataset! -  Location information is not considered! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 22.
    22 Related Works -  Event Clustering (Visual/Temporal information) [Loui, Savakis 2002] -  Albuming user photo collections -  Not scalable to large dataset! -  Limited to user photo collection! -  No Locational Information! -  Event/Place Semantic Identification (Temporal information) [Rattenbury et al. 2007] -  Extraction of event and place semantics for tags assigned to Flickr photos -  Scale-Structure Identification (SSI) method to analyze the tag usage distribution -  SSI is limited for large dataset! -  Location information is not considered! -  Event Tag Detection (Spatial/Temporal information) [Chen, Roy 2009] -  Detect event tags from Flickr photos -  As [Rattenbury et al. 2007] use SSI method to analyze the tag usage distribution -  SSI is used over locational and spatial distributions simultaneously Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 23.
    23 Problem Definition Hypothesis Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 24.
    24 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 25.
    25 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 26.
    26 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Event Cluster ej  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 27.
    27 Problem Definition Hypothesis Something happening in a certain place at a certain time [Yang, Pierce, Carbonell 1999] Something happening in a certain place at a certain time with a certain tag Event Cluster ej  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Not the opposite  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 28.
    28 Problem Definition Hypothesis – Landmark clusters Location Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 29.
    29 Problem Definition Hypothesis – Landmark clusters Location Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 30.
    30 Problem Definition Hypothesis – Landmark clusters Landmark Location Clusters Event Cluster ek … {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g colosseo! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Not the opposite  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 31.
    31 Problem Definition Hypothesis – Event clusters Location g time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 32.
    32 Problem Definition Hypothesis – Event clusters Location g dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 33.
    33 Problem Definition Hypothesis – Event clusters Location g applepies! dt time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 34.
    34 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 35.
    35 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! dt time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } The opposite is true  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 36.
    36 Problem Definition Hypothesis – Event clusters Landmark Clusters Location Event Cluster ek Event Clusters {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } g applepies! time Event Cluster ek  {tj=tj, dti=dtj, gi=gj, Ii,Ij ek } The opposite is true  ! Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 37.
    37 Problem Definition New Formulation Event Event Cluster ek Clusters Location Sdgt Location Sgt = g applepies! g applepies! dt time time Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 38.
    38 Problem Definition New Formulation Event Event Cluster ek Clusters { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) Location Sdgt € Location Sgt = g applepies! g applepies! dt time time Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 39.
    39 Preliminary Suffix-Tree Clustering [Zamir 1998] Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 40.
    40 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 41.
    41 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 42.
    42 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 43.
    43 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 44.
    44 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 45.
    45 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 46.
    46 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model -  Snippet-tolerant Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 47.
    47 Preliminary Suffix-Tree Clustering [Zamir 1998] -  Suffix-Tree based -  Mainly used in text (web) document clustering -  Three step process: 1  Document cleaning 2  Base clusters identification 3  Base clusters merging -  Incremental clustering -  Cluster label inferred by the tree structure -  Phrase-Based model -  Snippet-tolerant -  Overlapped clusters Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 48.
    48 Preliminary Suffix-Tree Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 49.
    49 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 50.
    50 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Papua ‘apua’ ‘pua’ ‘ua’ ‘a’ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 51.
    51 Preliminary Suffix-Tree -  Given a string S suffix-tree is a Compact Trie containing all the suffixes of S -  Rooted directed tree -  Each internal node other than root has at least two children -  Each edge leaving a particular node is labelled with a non-empty substring of S Papua ‘apua’ ‘pua’ ‘ua’ ‘a’ -  Suffix-Tree construction performs in linear time (O(n)) ([Ukkonen 1995]) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 52.
    52 Algorithm Overview Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 53.
    53 Algorithm Overview Data cleaning Data extension Suffix Tree Construction Ii = (T, g, dt) Event clusters extraction Event Clusters merge … Primary! Party! Election! Campaign! … Concert! Music! John! … … Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 54.
    54 Algorithm Overview Data Cleaning and Extension Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 55.
    55 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 56.
    56 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 57.
    57 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] where s1 and s2 encoding function from date/location to string Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 58.
    58 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 59.
    59 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string acmm2010 26Oct2010 43.77:11.24 acmm2010 florence 26Oct2010 43.77:11.24 florence multimedia 26Oct2010 43.77:11.24 multimedia Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 60.
    60 Algorithm Overview Data Cleaning and Extension -  Cleaning: Ii = (T,g,dt)  Ii’ = (T’,g,dt) -  Stopword removal (with extended vocabulary) + Stemming -  Extension: Ii’ = (T’,g,dt)  Ii’’ = (T’’,g,dt) -  Spatial and Temporal information are encoded in the annotation set T T’’ = {t’’1, …, t’’l } s1 and s2 define the t’’i = [s1(dt) + s2(g) + ti ] granularity in space (geographical grid) and time where s1 and s2 encoding function from date/location to string acmm2010 26Oct2010 43.77:11.24 acmm2010 T’ florence T’’ 26Oct2010 43.77:11.24 florence multimedia 26Oct2010 43.77:11.24 multimedia s1(26/10/2010) s2(43.777864,11.249029) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 61.
    61 Algorithm Overview ST Construction and Event Extraction Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 62.
    62 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 63.
    63 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 64.
    64 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 65.
    65 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 66.
    66 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 67.
    67 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l -  IF (Ψl = Ψ’l)  Ψl ([s1(dt) + s2(g) + ti ]) is event cluster € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 68.
    68 Algorithm Overview ST Construction and Event Extraction -  Image Ii’’ : document snippet Ii’’ = (T’’,g,dt) T’’ = {t’’1, …, t’’l } t’’i = [s1(dt) + s2(g) + ti ] Ψ’l -  Extract Candidate event clusters Ψl : Ψl -  Ψl ([s1(dt) + s2(g) + ti ]) Event Cluster ek  { ∃ (dt, g, t) : Sdgt = Sgt} with (Sdgt = ek) -  Extract Ψ’l ([s2(g) + ti ]) -  Compare Ψl and Ψ’l -  IF (Ψl = Ψ’l)  Ψl ([s1(dt) + s2(g) + ti ]) is event cluster € -  Label inferred from the structure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 69.
    69 Algorithm Overview Extraction and Merge Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 70.
    70 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 71.
    71 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} -  Merge semantically similar cluster: Ψ’l Ψl Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 72.
    72 Algorithm Overview Extraction and Merge -  Extracted event clusters : {e1, …,en} -  Merge semantically similar cluster: ei ∩ e j Ψ’l θ (ei ,e j ) = min(ei ,e j ) Ψl € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 73.
    73 Evaluation - Dataset Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 74.
    74 Evaluation - Dataset -  Dataset collected from Flickr -  Only geo-tagged picture -  12 June 2008 – 11 June 2010 (729 days) -  San Francisco Area #Images ~ 350K #Tags ~ 3M Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 75.
    75 Evaluation - Measure Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 76.
    76 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 77.
    77 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 78.
    78 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 79.
    79 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Rk Rk : relevant clusters in the Top-K Precision : first k returned K € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 80.
    80 Evaluation - Measure -  List of ranked Clusters: {e1, e2, …} -  Ranking according to cluster's size: |ei| -  Drawback: lack of ground truth (recall measure) Rk Rk : relevant clusters in the Top-K Precision : first k returned K Top-20 (K=20) € Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 81.
    81 Evaluation -  Experiment on different granularity in time and space -  Time: 1 day 1 week Example 2008Oct12 2008:43 -  Space: Latitude Precision Longitude Square Size Precision (Meters) 0.01 0.01 1000m X 1000m 0.005 0.005 500m X 500m 0.002 0.002 200m X 200m 0.001 0.001 100m X 100m Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 82.
    82 Evaluation - Results 100 m 200 m 500 m 1000 m 1 Day 1 Week 1 Day 1 Week 1 Day 1 Week 1 Day 1 Week #Clusters #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. #Ev. Prec. 1 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 1 100% 2 2 100% 2 100% 2 100% 2 100% 2 100% 2 100% 2 100% 1 50% 3 3 100% 3 100% 3 100% 3 100% 3 100% 3 100% 3 100% 2 67% … 20 15 75% 14 70% 15 75% 14 70% 14 70% 13 65% 13 65% 14 70% Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 83.
    83 Evaluation - Results Top-20 precision Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 84.
    84 Conclusion Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 85.
    85 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 86.
    86 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 87.
    87 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 88.
    88 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 89.
    89 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 90.
    90 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal -  Spatial and Time information considered Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 91.
    91 Conclusion -  Novel algorithm for event cluster extraction: -  from large amount of Flickr images -  Multi-user photo collection -  Incremental clustering algorithm -  Extension of STC previously used only to cluster text documents -  Based on a Suffix-Tree (construction O(n)) -  Automatic annotation of clusters -  Noise reduction in the tag using extended vocabulary for stopword removal -  Spatial and Time information considered -  Analysis of different granularity of time and space Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 92.
    92 Thanks ( ) for the attention! http://www.idi.ntnu.no/~ruocco/ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010
  • 93.
    93 Thanks ( ) for the attention! QUESTIONS? http://www.idi.ntnu.no/~ruocco/ Massimiliano Ruocco – Event Cluster Detection on Flickr Images using a Suffix-Tree Structure – IEEE ISM2010