Visual Encoding Approaches for Temporal Social Networks Peter John Hoek BIT (Distinction) CQU, MSc (IT) UNSW A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Information Technology at the School of Engineering and Information Technology The University of New South Wales at the Australian Defence Force Academy 2013 Abstract Visualisations have become an inseparable part of social network analysis methodologies. However, despite the large amount of work in the field of social network visualisation there are still a number of areas in which current visualisation methods can be improved. The current dynamic network visualisation approaches consisting of aggregation or animated movies suffer from various limitations, such as introducing artefacts that could obscure interesting micro-level patterns or disrupting the users’ internalised mental models. In addition, very few social network tools support the inclusion of semantic and contextual information or provide visual topological representations based on network node attributes. This thesis introduces novel approaches to the visualisation of social networks and assesses their effectiveness through the use of concept demonstrators and prototypes. These are the software artefacts of this thesis, which provide illustrations of complementary visualisation techniques that could be considered for inclusion into social network visualisation and analysis tools. The novel methods for visualising temporal networks introduced in this thesis consist of: i an Attribute-Based Graph Visualisation (ABGV) approach for introducing attributes as additional nodes of the sociogram, a visual component for the Social Network Analysis for Command and Control (SNAC2) tool, useful for visualising the changing topology of the network at the same time with the contextual source of the links in the network, a Parallel Arc Diagram Visualisation method and a software prototype the Temporal Interactive Parallel Arc Diagram (TIPAD) for discovering temporal patterns embedded in the network, and a prototype for the Temporal Interactive Multi-slider Event and Relationship (TIMER) that combines node-link representations with representations of events in time without aggregation or animation, the main purpose of which is to preserve information faithfulness. In addition this thesis extends the standard static taxonomic tasks with temporal tasks descriptions for the purpose of enhancing the evaluation of temporal visualisation techniques. The performance of the proposed methods was tested using a combination of case studies, publicly-available datasets and the features of the proposed methods compared with established tools. A taxonomic evaluation provides the basis for positioning the proposed methods within the social network visualisation domain. ii Acknowledgments Social network theory suggests everyone connected to me has in some way influenced my research. I am therefore very grateful to all the people in my social network. I am especially grateful to my supervisors Dr Hussein Abbass and Dr Michael Sweeney for their patience and support throughout this journey. Mike’s continued encouragement drove me to complete this thesis. This work was enabled through the support of the Defence Study Bank scheme which provided both financial support and leave to pursue this research. I wish to acknowledge my son, Keeley, for all his work in assisting me with the preparation of Adobe Flash animations for journal papers and his assistance in coding the TIMER tool. Most of all I appreciate the time he made for our discussions and his ongoing encouragement. I would also like to thank my son Kai for allowing me the time to write this thesis when he really wanted me to do something “fun” with him. Most of all I wish to thank my wife Mellissa for all her support and encouragement. Without her continued support and understanding I would not have been able to undertake this research. The software prototypes discussed in this thesis were constructed through the use of the Java programming language. The screenshots of some of the prototypes and other images presented herein were often created by programs iii utilising the Perfuse and Jung programming libraries. I therefore wish to thank both of those software development communities for their great work and their efforts in maintaining these very useful toolkits and especially those that have contributed to the theoretical underpinnings which often is overlooked. iv Introduction Table of contents ABSTRACT I ACKNOWLEDGMENTS III TABLE OF CONTENTS 1 LIST OF FIGURES 5 LIST OF TABLES 9 LIST OF ABBREVIATIONS 10 CHAPTER 1. INTRODUCTION 11 1.1 Social Networks 12 1.2 Social Network Visualisation 14 1.3 Challenges 16 1.4 Research Aims and Approach 21 1.5 Scope 22 1.6 Contributions 25 1.7 Thesis Structure 27 CHAPTER 2. BACKGROUND 33 2.1 Visualisation 33 2.2 Social Network Visualisation 36 2.3 Social Network Analysis 43 2.4 Fundamental Algorithmic Approaches to Visualisation 50 2.4.1 Force-Directed Methods 51 2.4.2 Non-Euclidean Approaches 55 2.4.3 Hierarchical Approaches 56 1 Introduction 2.4.4 Orthogonal Graph Drawing 61 2.4.5 Matrix Representations 62 2.4.6 Arc Diagrams 64 2.4.7 Radial Layout 64 2.4.8 Circular Layout 65 2.4.9 Algorithm Summary 66 2.5 Enhancing Social Network Visualisation 69 2.5.1 Node-link Aesthetics 71 2.5.2 Alternatives to Node-link diagrams 73 2.5.3 Analytical User-Centred Visualisation 75 2.6 High-level Approaches to Social Network Visualisation 78 2.6.1 Visualising Clusters (Communities) 78 2.6.2 Dynamic Network Visualisation 88 2.6.3 Visualising Semantics and Attributes 117 2.7 Studies and Evaluation 135 CHAPTER 3. ATTRIBUTE BASED GRAPH VISUALISATION (ABGV) 143 3.1 Background 144 3.2 Motivation and Inspiration 146 3.3 Technique 148 3.4 Data Structures and Design Choices 153 3.5 Discussion 154 3.6 Evaluation 156 3.7 Implementation 159 3.7.1 Data 159 3.7.2 Program Code 161 3.8 Summary and Conclusion 163 CHAPTER 4. SOCIAL NETWORK ANALYSIS FOR COMMAND AND CONTROL (SNAC2) 165 4.1 Background 167 4.2 Similar Work 171 4.2.1 Continuous Node-Link Layout 173 4.3 Event Based Analysis + Content 175 2 Introduction 4.4 Implementation 177 4.4.1 Data 178 4.4.2 Program Code 180 4.5 User Evaluation 181 4.6 Concluding Remarks 186 CHAPTER 5. THE PARALLEL ARC DIAGRAM (PAD) 188 5.1 Background 189 5.2 PAD Concept 191 5.3 Evaluation Taxonomy 198 5.4 Temporal Interactive Parallel Arc Diagram (TIPAD) 200 5.4.1 Similar Work 201 5.4.2 The Script and the Network 202 5.4.3 Comparative Visualisations 204 5.4.4 TIPAD Design and Operation 209 5.5 Implementation 220 5.5.1 Data 220 5.5.2 Program Code 221 5.6 Conclusion 222 CHAPTER 6. TEMPORAL INTERACTIVE MULTI-SLIDER EVENT AND RELATIONSHIP (TIMER) TOOL 228 6.1 The Dataset 229 6.2 Similar Work 232 6.3 Motivation 237 6.4 TIMER Approach 237 6.5 Evaluating the Prototype 240 6.6 Discussion 246 6.7 Implementation 249 6.7.1 Program Code 249 CHAPTER 7. PROTOTYPES EVALUATION 254 3 Introduction 7.1 Evaluation 258 7.1.1 Object Focus 260 7.1.2 Low Level Tasks 262 7.1.3 Topology-based Tasks 277 7.1.4 Attribute-based Tasks 284 7.1.5 Browsing Tasks 287 7.1.6 Overview 289 7.1.7 Temporal Task Evaluation 296 7.1.8 Faithfulness 303 CHAPTER 8. CONCLUSIONS AND FUTURE WORK 308 8.1 ABGV 310 8.2 SNAC2 313 8.3 TIPAD 315 8.4 TIMER 317 REFERENCES 319 APPENDIX A - GLOSSARY 354 APPENDIX B – PSEUDO CODE & CLASS DIAGRAM 360 ABGV 360 SNAC2 364 TIPAD 367 TIMER 370 4 Introduction List of Figures FIGURE 1 –HUMANS NATURALLY USE NODE-LINK DIAGRAMS TO DESCRIBE RELATED CONCEPTS .... 18 FIGURE 2 – DIFFERENT PATHS ARE EMPHASISED DESPITE NODES POSITIONED IN THE SAME LOCATION [ADAPTED FROM (WARE 2000)] ............................................................................... 19 FIGURE 3 - THESIS CONTRIBUTIONS IN THE SOCIAL NETWORK VISUALISATION SPACE ...................... 30 FIGURE 4 - VAN WIJK MODEL OF VISUALISATION (VAN WIJK 2005; VAN WIJK 2006) ......................... 34 FIGURE 5 - VISUALISATION TAXONOMY .............................................................................................. 35 FIGURE 6 -MORENO'S HAND DRAWN SOCIOGRAM: THIS NODE-LINK DIAGRAM PUBLISHED IN THE NEW YORK TIMES IN 1933 BY JACOB MORENO SHOWS RELATIONSHIPS BETWEEN FOURTH GRADERS. .................................................................................................................................... 36 FIGURE 7 - A SOCIAL NETWORK DIAGRAM. SOURCE: ORGNET.COM (IMAGE REPRODUCED WITH KIND PERMISSION OF VALDIS KREBS) .................................................................................................. 37 FIGURE 8 -SAMPLES OF SOCIAL NETWORK VISUALISATION TOOLS. SOURCE VISUALCOMPLEXITY.COM .................................................................................................................................................... 42 FIGURE 9 - PRIMARY ELEMENTS FOR VISUAL GRAPH ANALYSIS (VON LANDESBERGER, KUIJPER ET AL. 2011) ........................................................................................................................................... 50 FIGURE 10 -AN EXAMPLE OF THE SUGIYAMA LAYOUT ........................................................................ 57 FIGURE 11 – (A) A DIGRAPH AND (B) THE SAME GRAPH DRAWN WITH THE SUGIYAMA ALGORITHM (ADAPTED FROM (HEALY AND NIKOLOV 2013) .......................................................................... 59 FIGURE 12 – TWO ALTERNATIVE DRAWINGS OF THE SAME NETWORK. (A) FORCE DIRECTED (B) SUGIYAMA (HEALY AND NIKOLOV 2013) ...................................................................................