261 research outputs found
4-labelings and grid embeddings of plane quadrangulations
We show that each quadrangulation on vertices has a closed rectangle of influence drawing on the grid.
Further, we present a simple algorithm to obtain a straight-line drawing of a quadrangulation on the
grid.
This is not optimal but has the advantage over other existing algorithms that it is not needed to add edges to
the quadrangulation to make it -connected.
The algorithm is based on angle labeling and simple face counting in regions analogous to Schnyder's grid embedding for triangulation.
This extends previous results on book embeddings for quadrangulations from Felsner, Huemer, Kappes, and Orden (2008).
Our approach also yields a representation of a quadrangulation as a pair of rectangulations with a curious property
Planar projections of graphs
We introduce and study a new graph representation where vertices are embedded
in three or more dimensions, and in which the edges are drawn on the
projections onto the axis-parallel planes. We show that the complete graph on
vertices has a representation in planes. In 3
dimensions, we show that there exist graphs with edges that can be
projected onto two orthogonal planes, and that this is best possible. Finally,
we obtain bounds in terms of parameters such as geometric thickness and linear
arboricity. Using such a bound, we show that every graph of maximum degree 5
has a plane-projectable representation in 3 dimensions.Comment: Accepted at CALDAM 202
Helmholtz Portfolio Theme Large-Scale Data Management and Analysis (LSDMA)
The Helmholtz Association funded the "Large-Scale Data Management and Analysis" portfolio theme from 2012-2016. Four Helmholtz centres, six universities and another research institution in Germany joined to enable data-intensive science by optimising data life cycles in selected scientific communities. In our Data Life cycle Labs, data experts performed joint R&D together with scientific communities. The Data Services Integration Team focused on generic solutions applied by several communities
Flud: a hybrid crowd-algorithm approach for visualizing biological networks
Modern experiments in many disciplines generate large quantities of network
(graph) data. Researchers require aesthetic layouts of these networks that
clearly convey the domain knowledge and meaning. However, the problem remains
challenging due to multiple conflicting aesthetic criteria and complex
domain-specific constraints. In this paper, we present a strategy for
generating visualizations that can help network biologists understand the
protein interactions that underlie processes that take place in the cell.
Specifically, we have developed Flud, an online game with a purpose (GWAP) that
allows humans with no expertise to design biologically meaningful graph layouts
with the help of algorithmically generated suggestions. Further, we propose a
novel hybrid approach for graph layout wherein crowdworkers and a simulated
annealing algorithm build on each other's progress. To showcase the
effectiveness of Flud, we recruited crowd workers on Amazon Mechanical Turk to
lay out complex networks that represent signaling pathways. Our results show
that the proposed hybrid approach outperforms state-of-the-art techniques for
graphs with a large number of feedback loops. We also found that the
algorithmically generated suggestions guided the players when they are stuck
and helped them improve their score. Finally, we discuss broader implications
for mixed-initiative interactions in human computation games.Comment: This manuscript is currently under revie
Automatisches Zeichnen von Graphen fĂŒr modellgetriebene Softwareentwicklung
As shown previously by Fuhrmann, there are several concepts for increasing the productivity of MDE by improving the practical handling of models. The automatic layout of graph-based models is a key enabler in this context. However, there is a striking contrast between the abundance of research results in the field of graph layout methods and the current state of graphical modeling tools, where only a tiny fraction of these results are ever adopted. This thesis aims to bridge this gap on three separate levels: specialized layout algorithms, configuration management, and software infrastructure. Regarding layout algorithms, here we focus on the layer-based approach. We examine its extension to include ports and hyperedges, which are essential features of certain kinds of graphs, e.g. data flow models. The main contribution is the handling of constraints on the positioning of ports, which is done mainly in the crossing minimization and edge routing phases. Hyperedges are represented with normal edges, simplifying their handling but introducing inaccuracies for counting crossings. A final extension discussed here is a sketch-driven approach for simple integration of user interactivity. An abstract layout is the selection of a layout algorithm with a mapping of its parameters to specific values. We discuss a new meta model allowing to specify the structure of a graph as well as its abstract layout and its concrete layout, i.e. positioning data computed by the layout algorithm. This forms a basis for efficient management of layout configurations. Furthermore, we investigate an evolutionary algorithm for searching the solution space of abstract layouts, taking readability criteria into account for evaluating solutions. The software infrastructure developed here targets the connection of arbitrary diagram viewers (front-ends) with arbitrary graph layout algorithms (back-ends). The main challenge is to find suitable abstractions that allow such generality and at the same time keep the complexity as low as possible. We discuss a possible realization based on the Eclipse platform, which is used by several modeling tools, e.g. the Graphical Modeling Framework. A web-based survey has been conducted among users of the layout infrastructure in order to evaluate to what extent the stated goals have been met. The overall feedback collected from this survey is very positive.Wie bereits von Fuhrmann gezeigt, kann die ProduktivitĂ€t modellgetriebener Softwareentwicklung durch zahlreiche Konzepte zur Verbesserung der praktischen Handhabung von Modellen erhöht werden. Dabei ist das automatische Layout graphenbasierter Modelle ein zentraler SchlĂŒssel. Allerdings gibt es einen bemerkenswerten Kontrast zwischen der FĂŒlle an Forschungsergebnissen im Bereich des Graphen-Layout und dem aktuellen Stand graphischer Modellierungswerkzeuge, bei denen nur ein kleiner Teil dieser Ergebnisse ĂŒbernommen wird. Das Ziel dieser Arbeit ist diese LĂŒcke auf drei separaten Ebenen zu ĂŒberbrĂŒcken: spezialisierte Layout-Algorithmen, Verwaltung von Konfigurationen und Software-Infrastruktur. Im Bezug auf Layout-Algorithmen liegt der Schwerpunkt auf dem Layer-basierten Ansatz. Wir untersuchen dessen Erweiterung zur UnterstĂŒtzung von Ports und Hyperkanten, was wesentliche Bestandteile bestimmter Arten von Graphen sind, z.B. Datenflussmodelle. Der Hauptbeitrag ist die Einbeziehung von Bedingungen fĂŒr die Positionierung von Ports, vor allem wĂ€hrend der Kreuzungsminimierung und der KantenfĂŒhrungsphase. Hyperkanten werden durch normale Kanten reprĂ€sentiert, was deren Verarbeitung vereinfacht aber Ungenauigkeiten beim ZĂ€hlen von Kreuzungen verursacht. Als letzte Erweiterung betrachten wir einen Sketch-basierten Ansatz fĂŒr die einfache Integration von NutzerinteraktivitĂ€t. Ein abstraktes Layout ist die Auswahl eines Layout-Algorithmus zusammen mit einer Abbildung seiner Parameter auf konkrete Werte, wĂ€hrend ein konkretes Layout Positionsdaten beschreibt, die von einem Algorithmus berechnet wurden. Wir diskutieren ein neues Metamodell, mit dem sowohl die Struktur als auch das abstrakte sowie das konkrete Layout eines Graphen spezifiziert werden kann. Dies bildet eine Grundlage fĂŒr die effiziente Verwaltung von Layout-Konfigurationen. Zudem untersuchen wir einen evolutionĂ€ren Algorithmus fĂŒr die Suche im Lösungsraum abstrakter Layouts, wobei zur Bewertung von Lösungen Ăsthetikkriterien ausgewertet werden. Die in dieser Arbeit entwickelte Software-Infrastruktur hat als Ziel, beliebige Graphen-basierte Diagramme (front-ends) mit beliebigen Layout-Algorithmen (back-ends) zu verbinden. Die gröĂte Herausforderung dabei ist das Finden geeigneter Abstraktionen, die eine solche AllgemeingĂŒltigkeit erlauben und gleichzeitig die KomplexitĂ€t so niedrig wie möglich halten. Wir betrachten eine mögliche Realisierung, die auf Eclipse basiert, eine von vielen Modellierungswerkzeugen verwendete Plattform. Eine Web-basierte Umfrage wurde unter Nutzern der Layout-Infrastruktur durchgefĂŒhrt, um zu untersuchen inwieweit die gesteckten Ziele erfĂŒllt worden sind. Die allgemeine Resonanz zu dieser Umfrage ist sehr positiv
On the Parameterized Complexity of Computing Tree-Partitions
We study the parameterized complexity of computing the tree-partition-width,
a graph parameter equivalent to treewidth on graphs of bounded maximum degree.
On one hand, we can obtain approximations of the tree-partition-width
efficiently: we show that there is an algorithm that, given an -vertex graph
and an integer , constructs a tree-partition of width for
or reports that has tree-partition width more than , in time
. We can improve on the approximation factor or the dependence on
by sacrificing the dependence on .
On the other hand, we show the problem of computing tree-partition-width
exactly is XALP-complete, which implies that it is -hard for all . We
deduce XALP-completeness of the problem of computing the domino treewidth.
Finally, we adapt some known results on the parameter tree-partition-width and
the topological minor relation, and use them to compare tree-partition-width to
tree-cut width
Making machine intelligence less scary for criminal analysts: reflections on designing a visual comparative case analysis tool
A fundamental task in Criminal Intelligence Analysis is to analyze the similarity of crime cases, called CCA, to identify common crime patterns and to reason about unsolved crimes. Typically, the data is complex and high dimensional and the use of complex analytical processes would be appropriate. State-of-the-art CCA tools lack flexibility in interactive data exploration and fall short of computational transparency in terms of revealing alternative methods and results. In this paper, we report on the design of the Concept Explorer, a flexible, transparent and interactive CCA system. During this design process, we observed that most criminal analysts are not able to understand the underlying complex technical processes, which decrease the users' trust in the results and hence a reluctance to use the tool}. Our CCA solution implements a computational pipeline together with a visual platform that allows the analysts to interact with each stage of the analysis process and to validate the result. The proposed Visual Analytics workflow iteratively supports the interpretation of the results of clustering with the respective feature relations, the development of alternative models, as well as cluster verification. The visualizations offer an understandable and usable way for the analyst to provide feedback to the system and to observe the impact of their interactions. Expert feedback confirmed that our user-centred design decisions made this computational complexity less scary to criminal analysts
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