Institut für Wirtschaftsinformatik
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Publikation On the impact of using utilities rather than costs for graph matching(Springer, 09.11.2019) Riesen, Kaspar; Bunke, Horst; Fischer, AndreasThe concept of graph edit distance constitutes one of the most flexible graph matching paradigms available. The major drawback of graph edit distance, viz. the exponential time complexity, has been recently overcome by means of a reformulation of the edit distance problem to a linear sum assignment problem. However, the substantial speed up of the matching is also accompanied by an approximation error on the distances. Major contribution of this paper is the introduction of a transformation process in order to convert the underlying cost model into a utility model. The benefit of this transformation is that it enables the integration of additional information in the assignment process.We empirically confirm the positive effects of this transformation on five benchmark graph sets with respect to the accuracy and run time of a distance based classifier.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Approximate graph edit distance in quadratic time(IEEE, 2020) Riesen, Kaspar; Ferrer, Miquel; Bunke, HorstGraph edit distance is one of the most flexible and general graph matching models available. The major drawback of graph edit distance, however, is its computational complexity that restricts its applicability to graphs of rather small size. Recently, the authors of the present paper introduced a general approximation framework for the graph edit distance problem. The basic idea of this specific algorithm is to first compute an optimal assignment of independent local graph structures (including substitutions, deletions, and insertions of nodes and edges). This optimal assignment is complete and consistent with respect to the involved nodes of both graphs and can thus be used to instantly derive an admissible (yet suboptimal) solution for the original graph edit distance problem in Ο(n³) time. For large scale graphs or graph sets, however, the cubic time complexity may still be too high. Therefore, we propose to use suboptimal algorithms with quadratic rather than cubic time for solving the basic assignment problem. In particular, the present paper introduces five different greedy assignment algorithms in the context of graph edit distance approximation. In an experimental evaluation, we show that these methods have great potential for further speeding up the computation of graph edit distance while the approximated distances remain sufficiently accurate for graph based pattern classification.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Approximation of Graph Edit Distance in Quadratic Time(05/2015) Riesen, Kaspar; Ferrer, Miquel; Fischer, Andreas; Bunke, HorstThe basic idea of a recent graph matching framework is to reduce the problem of graph edit distance (GED) to an instance of a linear sum assignment problem (LSAP). The optimal solution for this simplified GED problem can be computed in cubic time and is eventually used to derive a suboptimal solution for the original GED problem. Yet, for large scale graphs and/or large scale graph sets the cubic time complexity remains a severe handicap of this procedure. Therefore, we propose to use suboptimal algorithms – with quadratic rather than cubic time complexity – for solving the underlying LSAP. In particular, we introduce several greedy assignment algorithms for approximating GED. In an experimental evaluation we show that there is great potential for further speeding up the GED computation. Moreover, we empirically confirm that the distances obtained by this procedure remain sufficiently accurate for graph based pattern classification.04B - Beitrag KonferenzschriftPublikation Improving bipartite graph edit distance approximation using various search strategies(04/2015) Riesen, Kaspar; Bunke, HorstRecently the authors of the present paper introduced an approximation framework for the graph edit distance problem. The basic idea of this approximation is to first build a square cost matrix C=(cij)C=(cij), where each entry cij reflects the cost of a node substitution, deletion or insertion plus the matching cost arising from the local edge structure. Based on C an optimal assignment of the nodes and their local structure can be established in polynomial time. Since this approach considers local – rather than the global – structural properties of the graphs only, the graph edit distance derived from the optimal node assignment generally overestimates the true edit distance. The present paper pursues the idea of applying additional search strategies that build upon the initial assignment in order to reduce this overestimation. To this end, six different search strategies are investigated in this paper. In an exhaustive experimental evaluation on five real world graph data sets we empirically verify a substantial gain of distance accuracy by means of all search methods while run time remains remarkably low. Keywords Bipartite graph matching; Approximate graph edit distance01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Suboptimal Graph Edit Distance Based on Sorted Local Assignments(Springer, 2015) Riesen, Kaspar; Ferrer, Miquel; Bunke, Horst; Schwenker, Friedhelm; Roli, Fabio; Kittler, JosephGraph based pattern representation offers a number of useful properties. In particular, graphs can adapt their size and complexity to the actual pattern, and moreover, graphs are able to describe structural relations that might exist within a pattern. Yet, the high representational power and flexibility of graphs is accompanied by a significant increase of the complexity of many algorithms. For instance, exact computation of pairwise graph distance can be accomplished in exponential time complexity only. A previously introduced approximation framework reduces the problem of graph distance computation to an instance of a linear sum assignment problem. This allows suboptimal graph distance computation in cubic time. The present paper introduces a novel procedure, which is conceptually related to this previous approach, but offers O(n2log(n2)) (rather than cubic) run time. We empirically verify the speed up of our novel approximation and show that the faster approximation is able to keep up with the existing framework with respect to distance accuracy.04B - Beitrag KonferenzschriftPublikation Estimating Graph Edit Distance Using Lower and Upper Bounds of Bipartite Approximations(World Scientific, 02.03.2015) Riesen, Kaspar; Fischer, Andreas; Bunke, HorstThe concept of graph edit distance (GED) is still one of the most flexible and powerful graph matching approaches available. Yet, exact computation of GED can be solved in exponential time complexity only. A previously introduced approximation framework reduces the computation of GED to an instance of a linear sum assignment problem. Major benefit of this reduction is that an optimal assignment of nodes (including local structures) can be computed in polynomial time. Given this assignment an approximate value of GED can be immediately derived. Yet, this approach considers local — rather than the global — structural properties of the graphs only, and thus GED derived from the optimal node assignment generally overestimates the true edit distance. Recently, it has been shown how the existing approximation framework can be exploited to additionally derive a lower bound of the exact edit distance without any additional computations. In this paper we make use of regression analysis in order to predict the exact GED using these two bounds. In an experimental evaluation on diverse graph data sets we empirically verify the gain of distance accuracy of the estimated GEDs compared to both bounds.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Novel Kernels for Error-tolerant Graph Classification(Brill, 2009) Riesen, Kaspar; Bunke, Horst; Neuhaus, Michel01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Non-linear Transformations of Vector Space embedded Graphs(2008) Riesen, Kaspar; Bunke, Horst; Juan-Ciscar, Alfons; Sanchez, Gemma04B - Beitrag KonferenzschriftPublikation Graph Classification by means of Lipschitz Embedding(IEEE, 2009) Riesen, Kaspar; Bunke, Horst01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Feature Ranking Algorithms for Improving Classification of Vector Space Embedded Grahps(Springer, 2009) Bunke, Horst; Riesen, Kaspar; Jiang, Xiaoyi; Petkov, Nicolai04B - Beitrag Konferenzschrift