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11
IPSepCoLa: An incremental procedure for separation constraint layout of graphs
 IEEE TRANSACTIONS ON VISUALISATION AND COMPUTER GRAPHICS
, 2006
"... We extend the popular forcedirected approach to network (or graph) layout to allow separation constraints, which enforce a minimum horizontal or vertical separation between selected pairs of nodes. This simple class of linear constraints is expressive enough to satisfy a wide variety of applicati ..."
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Cited by 27 (12 self)
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We extend the popular forcedirected approach to network (or graph) layout to allow separation constraints, which enforce a minimum horizontal or vertical separation between selected pairs of nodes. This simple class of linear constraints is expressive enough to satisfy a wide variety of applicationspecific layout requirements, including: layout of directed graphs to better show flow; layout with nonoverlapping node labels; and layout of graphs with grouped nodes (called clusters). In the stress majorization forcedirected layout process, separation constraints can be treated as a quadratic programming problem. We give an incremental algorithm based on gradient projection for efficiently solving this problem. The algorithm is considerably faster than using generic constraint optimization techniques and is comparable in speed to unconstrained stress majorization. We demonstrate the utility of our technique with sample data from a number of practical applications including geneactivation networks, terrorist networks and visualization of highdimensional data.
Visualizing graphs  a generalized view
 In Proceedings of the conference on Information Visualization (IV’06
, 2006
"... The visualization of graphs has proven to be very useful for exploring structures in different application domains. However, in certain fields of computer science, graph visualization is understood and focused quite differently. While ”graph drawing ” focuses on optimized layouts for nodelinkrepres ..."
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Cited by 12 (2 self)
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The visualization of graphs has proven to be very useful for exploring structures in different application domains. However, in certain fields of computer science, graph visualization is understood and focused quite differently. While ”graph drawing ” focuses on optimized layouts for nodelinkrepresentations of networks, ”information visualization” prefers to work on hierarchies focusing on very large structures, different views and interactivity. This paper gives a systematic view of the problem of graph visualization by combining both approaches. We will introduce a general view of different visualization methods as well as describe occurring problems and discuss basic constraints. These will be used to propose a visualization framework for graphs, whose development motivated this paper.
Stress majorization with orthogonal ordering constraints
 In Proceedings of the 13th International Symposium on Graph Drawing (GD’05), volume 3843 of LNCS
, 2005
"... Abstract. The adoption of the stressmajorization method from multidimensional scaling into graph layout has provided an improved mathematical basis and better convergence properties for socalled “forcedirected placement ” techniques. In this paper we give an algorithm for augmenting such stress ..."
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Cited by 8 (5 self)
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Abstract. The adoption of the stressmajorization method from multidimensional scaling into graph layout has provided an improved mathematical basis and better convergence properties for socalled “forcedirected placement ” techniques. In this paper we give an algorithm for augmenting such stressmajorization techniques with orthogonal ordering constraints and we demonstrate several graphdrawing applications where this class of constraints can be very useful.
Effects of Sociogram Drawing Conventions and Edge Crossings in Social Network Visualization
 Journal of Graph Algorithms and Applications
, 2007
"... This paper describes a withinsubjects experiment. In this experiment, the effects of different spatial layouts on human sociogram perception are examined. We compare the relative effectiveness of five sociogram drawing conventions in communicating underlying network substance, based on user task pe ..."
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Cited by 6 (0 self)
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This paper describes a withinsubjects experiment. In this experiment, the effects of different spatial layouts on human sociogram perception are examined. We compare the relative effectiveness of five sociogram drawing conventions in communicating underlying network substance, based on user task performance and personal preference. We also explore the impact of edge crossings, a widely accepted readability aesthetic. Both objective performance and subjective questionnaire measures are employed in the study. Subjective data are gathered based on the methodology of Purchase et al. [70], while objective data are collected through an online system. We found that 1) both edge crossings and drawing conventions pose significant effects on user preference and task performance of finding groups, but neither has much impact on the perception of actor status. On the other hand, node positioning and angular resolution may be more important in perceiving actor status. In visualizing social networks, it is important to note that the techniques that are highly preferred by users do not necessarily lead to best task performance. 2) subjects have a strong preference of placing nodes on the top or in the center to highlight importance, and clustering nodes in the same group and separating clusters to highlight groups. They have tendency to believe that nodes on the top or in the center are more important, and nodes in close proximity belong to the same group. Some preliminary recommendations for sociogram design and hypotheses about human reading behavior are proposed.
Drawing directed graphs using quadratic programming
 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS
, 2006
"... We describe a new method for visualization of directed graphs. The method combines constraint programming techniques with a high performance forcedirected placement (FDP) algorithm. The resulting placements highlight hierarchy in directed graphs while retaining useful properties of FDP; such as em ..."
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Cited by 5 (4 self)
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We describe a new method for visualization of directed graphs. The method combines constraint programming techniques with a high performance forcedirected placement (FDP) algorithm. The resulting placements highlight hierarchy in directed graphs while retaining useful properties of FDP; such as emphasis of symmetries and preservation of proximity relations. Our algorithm automatically identifies those parts of the digraph that contain hierarchical information and draws them accordingly. Additionally, those parts that do not contain hierarchy are drawn at the same quality expected from a nonhierarchical, undirected layout algorithm. Our experiments show that this new approach is better able to convey the structure of large digraphs than the most widely used hierarchical graphdrawing method. An interesting application of our algorithm is directional multidimensional scaling (DMDS). DMDS deals with lowdimensional embedding of multivariate data where we want to emphasize the overall flow in the data (e.g., chronological progress) along one of the axes.
ImPrEd: An Improved ForceDirected Algorithm that Prevents Nodes from Crossing Edges
, 2011
"... PrEd [Ber00] is a forcedirected algorithm that improves the existing layout of a graph while preserving its edge crossing properties. The algorithm has a number of applications including: improving the layouts of planar graph drawing algorithms, interacting with a graph layout, and drawing Eulerli ..."
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Cited by 1 (0 self)
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PrEd [Ber00] is a forcedirected algorithm that improves the existing layout of a graph while preserving its edge crossing properties. The algorithm has a number of applications including: improving the layouts of planar graph drawing algorithms, interacting with a graph layout, and drawing Eulerlike diagrams. The algorithm ensures that nodes do not cross edges during its execution. However, PrEd can be computationally expensive and overlyrestrictive in terms of node movement. In this paper, we introduce ImPrEd: an improved version of PrEd that overcomes some of its limitations and widens its range of applicability. ImPrEd also adds features such as flexible or crossable edges, allowing for greater control over the output. Flexible edges, in particular, can improve the distribution of graph elements and the angular resolution of the input graph. They can also be used to generate Euler diagrams with smooth boundaries. As flexible edges increase data set size, we experience an execution/drawing quality trade off. However, when flexible edges are not used, ImPrEd proves to be consistently faster than PrEd. Categories and Subject Descriptors (according to ACM CCS): G.2.2 [Discrete Mathematics]: Graph Theory—Graph Algorithms
FeatureBased Graph Visualization
, 2008
"... A graph consists of a set and a binary relation on that set. Each element of the set is a node of the graph, while each element of the binary relation is an edge of the graph that encodes a relationship between two nodes. Graph are pervasive in many areas of science, engineering, and the social scie ..."
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Cited by 1 (0 self)
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A graph consists of a set and a binary relation on that set. Each element of the set is a node of the graph, while each element of the binary relation is an edge of the graph that encodes a relationship between two nodes. Graph are pervasive in many areas of science, engineering, and the social sciences: servers on the Internet are connected, proteins interact in large biological systems, social networks encode the relationships between people, and functions call each other in a program. In these domains, the graphs can become very large, consisting of hundreds of thousands of nodes and millions of edges. Graph drawing approaches endeavour to place these nodes in two or threedimensional space with the intention of fostering an understanding of the binary relation by a human being examining the image. However, many of these approaches to drawing do not exploit higherlevel structures in the graph beyond the nodes and edges. Frequently, these structures can be exploited for drawing. As an example, consider a large computer network where nodes are servers and edges are connections between those servers. If a user would like understand how servers at UBC connect to the rest of the network, a drawing that accentuates the set of nodes representing those servers may be more helpful than an approach where all nodes are drawn in the same way. In a featurebased approach, features are subgraphs exploited for the purposes of drawing. We endeavour to depict not only the binary relation, but the highlevel relationships between features. This thesis extensively explores a featurebased approach to graph visualization and demonstrates the viability of tools that aid in the visualization of large graphs. Our contributions lie in presenting and evaluating novel techniques and algorithms for graph visualization. We implement five systems in order to empirically evaluate these techniques and algorithms, comparing them to previous approaches.
VISUALIZING & EXPLORING NETWORKS USING SEMANTIC SUBSTRATES
, 2008
"... Visualizing and exploring network data has been a challenging problem for HCI (HumanComputer Interaction) Information Visualization researchers due to the complexity of representing networks (graphs). Research in this area has concentrated on improving the visual organization of nodes and links acc ..."
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Visualizing and exploring network data has been a challenging problem for HCI (HumanComputer Interaction) Information Visualization researchers due to the complexity of representing networks (graphs). Research in this area has concentrated on improving the visual organization of nodes and links according to graph drawing aesthetics criteria, such as minimizing link crossings and the longest link length. Semantic substrates offer a different approach by which node locations represent node attributes. Users define semantic substrates for a given dataset according to the dataset characteristics and the questions, needs, and tasks of users. The substrates are typically 25 nonoverlapping rectangular regions that meaningfully lay out the nodes of the network, based on the node attributes. Link visibility filters are provided to enable users to limit link visibility to those within or across regions. The reduced clutter and visibility of only selected links are designed to help users find meaningful relationships. This dissertation presents 5 detailed case studies (3 longterm and 2 shortterm) that report on sessions with professional users working on their own datasets using successive versions of the NVSS (Network Visualization by Semantic Substrates,
Social Network Analysis of an Online Melanoma Discussion Group
"... We have developed tools to explore social networks that share information in medical forums to better understand the unmet informational needs of patients and family members facing cancer treatments. We define metrics that demonstrate members discussing interleukin2 receive a stronger response from ..."
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We have developed tools to explore social networks that share information in medical forums to better understand the unmet informational needs of patients and family members facing cancer treatments. We define metrics that demonstrate members discussing interleukin2 receive a stronger response from the melanoma discussion group than a typical topic. The interleukin2 network has a different topology than the melanoma network, has a higher density, and its members are more likely to have a higher intimacy level with another member and a lower inquisitiveness level than a typical melanoma user. Members are more likely to join the interleukin2 network to answer a question than in the melanoma network (probability =.2 ±.05 pvalue=.001). Within the melanoma network 20 % of the questions posed to the community do not get an answer. In the interleukin2 network, 1.3 % of the questions (one question) do not get a response.