On aesthetics for user-sketched layouts of vertex-weighted graphs

© 2020, The Visualization Society of Japan. Abstract: Recent empirical works on graph drawing have investigated visual properties of graph drawings created by users based on adjacency lists of graphs as well as drawing behaviors. This is mainly done by asking participants to sketch these graphs on a tablet computer so that they can freely express their interpretation. However, previous works did not consider weighted vertices, i.e., assigning a weight to a vertex to reflect its importance. Therefore, we conducted an empirical study on graphs with weighted vertices. More specifically, this work conducts an experiment and analyzes characteristics of the final graph layouts, participants’ drawing processes and strategies and their drawing preferences. Results indicated that minimizing the number of edge crossings was still the most important aesthetic for participants, and that participants preferred the aesthetic of creating grid-like drawings in the condition with weighted vertices. Hence, this work suggested that aesthetics of minimizing number of edge crossings and creating grid-like patterns should be the main consideration for designing a graph drawing software application. Graphic abstract: [Figure not available: see fulltext.]

NiMo syntax: part 1

Many formalisms for the specification for concurrent and distributed systems have emerged. In particular considering boxes and strings approaches. Examples are action calculi, rewriting logic and graph rewriting, bigraphs. The boxes and string metaphor is addressed with different levels of granularity. One of the approaches is to consider a process network as an hypergraph. Based in this general framework, we encode NiMo nets as a class of Annotated hypergraphs. This class is defined by giving the alphabet and the operations used to construct such programs. Therefore we treat only editing operations on labelled hypergraphs and afterwards how this editing operation affects the graph. Graph transformation (execution rules) is not covered here.Postprint (published version

The state of the art in empirical user evaluation of graph visualizations

While graph drawing focuses more on the aesthetic representation of node-link diagrams, graph visualization takes into account other visual metaphors making them useful for graph exploration tasks in information visualization and visual analytics. Although there are aesthetic graph drawing criteria that describe how a graph should be presented to make it faster and more reliably explorable, many controlled and uncontrolled empirical user studies flourished over the past years. The goal of them is to uncover how well the human user performs graph-specific tasks, in many cases compared to previously designed graph visualizations. Due to the fact that many parameters in a graph dataset as well as the visual representation of them might be varied and many user studies have been conducted in this space, a state-of-the-art survey is needed to understand evaluation results and findings to inform the future design, research, and application of graph visualizations. In this paper, we classify the present literature on the topmost level into graph interpretation, graph memorability, and graph creation where the users with their tasks stand in focus of the evaluation not the computational aspects. As another outcome of this work, we identify the white spots in this field and sketch ideas for future research directions

Evolutionary Layout of Graph Transformation Sequences

Graph transformation is used in various different research areas and has been implemented in several tool environments. However, the layout of graph transformation sequences is often perceived as not optimal and remains to be a difficult task. This is partly due to the slightly different requirements for layouting graph transformation sequences compared to standard graph sequences. In this paper, we clearly define these special requirements and present a layout algorithm which fulfills them. This layout algorithm allows the user to keep track of changes during transformation steps by introducing a concept of node aging and protection of senior node positions in the layout. Furthermore, this layout algorithm introduces a concept of layout patterns. We extended the well-known spring embedder layout algorithm by these new concepts and implemented the new algorithm in AGG, an environment for Attributed Graph Grammars. The layout algorithm has been tested with various graph grammars. A brief outlook describes how this layout algorithm can also be used for different kinds of graph sequences, e.g. sequences of successively developing class diagrams

A New Approach for Visualizing UML Class Diagrams

UML diagrams have become increasingly important in the engineering and reengineering processes for software systems. Of particular interest are UML class diagrams whose purpose is to display class hierarchies (generalizations), associations, aggregations, and compositions in one picture. The combination of hierarchical and non-hierarchical relations poses a special challenge to a graph layout tool. Existing layout tools treat hierarchical and non-hierarchical relations either alike or as separate tasks in a two-phase process as in, e.g., cite{See97}. We suggest a new approach for visualizing UML class diagrams leading to a balanced mixture of the following aesthetic criteria: Crossing minimization, bend minimization, uniform direction within each class hierarchy, no nesting of one class hierarchy within another, orthogonal layout, merging of multiple inheritance edges, and good edge labelling. We have realized our approach within the graph drawing library GoVisual. Experiments show the superiority to state-of-the-art and industrial standard layouts

A New Approach for Visualizing UML Class Diagrams

UML diagrams have become increasingly important in the engineering and reengineering processes for software systems. Of particular interest are UML class diagrams whose purpose is to display class hierarchies (generalizations), associations, aggregations, and compositions in one picture. The combination of hierarchical and non-hierarchical relations poses a special challenge to a graph layout tool. Existing layout tools treat hierarchical and non-hierarchical relations either alike or as separate tasks in a two-phase process as in, e.g., cite{See97}. We suggest a new approach for visualizing UML class diagrams leading to a balanced mixture of the following aesthetic criteria: Crossing minimization, bend minimization, uniform direction within each class hierarchy, no nesting of one class hierarchy within another, orthogonal layout, merging of multiple inheritance edges, and good edge labelling. We have realized our approach within the graph drawing library GoVisual. Experiments show the superiority to state-of-the-art and industrial standard layouts

Flexible trees: Sketching tree layouts

We introduce Flexible Trees, a sketch-based layout adjustment technique. Although numerous tree layout algorithms exist, these algorithms are usually bound to fit within standard shapes such as rectangles, circles and triangles. In order to provide the possibility of interactively customizing a tree layout, we offer a free-form sketchbased interaction through which one can re-define the boundary constraints for the tree layouts by combining ray-line intersection and line segment intersection. Flexible Trees offer topology preserving adjustments; can be used with a variety of tree layouts; and offer a simple way of authoring tree layouts for infographic purposes