TY - JOUR A1 - Bang‐Jensen, Jørgen A1 - Bellitto, Thomas A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - On DP‐coloring of digraphs JF - Journal of Graph Theory N2 - DP‐coloring is a relatively new coloring concept by Dvořák and Postle and was introduced as an extension of list‐colorings of (undirected) graphs. It transforms the problem of finding a list‐coloring of a given graph with a list‐assignment to finding an independent transversal in an auxiliary graph with vertex set . In this paper, we extend the definition of DP‐colorings to digraphs using the approach from Neumann‐Lara where a coloring of a digraph is a coloring of the vertices such that the digraph does not contain any monochromatic directed cycle. Furthermore, we prove a Brooks’ type theorem regarding the DP‐chromatic number, which extends various results on the (list‐)chromatic number of digraphs. Y1 - 2025 U6 - https://doi.org/10.1002/jgt.22535 SN - 0364-9024 VL - 95 IS - 1 SP - 76 EP - 98 PB - Wiley ER - TY - JOUR A1 - Bang-Jensen, Jørgen A1 - Bellitto, Thomas A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Hajós and Ore Constructions for Digraphs JF - The Electronic Journal of Combinatorics Y1 - 2025 U6 - https://doi.org/10.37236/8942 SN - 1077-8926 VL - 27 IS - 1 PB - The Electronic Journal of Combinatorics ER - TY - JOUR A1 - Kostochka, Alexandr V. A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Generalized DP-colorings of graphs JF - Discrete Mathematics N2 - In the present paper we extend the following three coloring concepts for the class of finite undirected graphs having multiple edges but no loops. First of all, the generalized coloring concept, in which the same colored vertices of a graph induce a subgraph satisfying a prescribed graph property. Secondly, the concept of variable degeneracy, which was introduced by Borodin, Kostochka and Toft in 2000; this makes it possible to give a common generalization of the point partition number and the list chromatic number. Finally, the DP-coloring concept as introduced by Ďvorák and Postle in 2018, where a list assignment of a graph is replaced by a cover. Combining these three coloring concepts leads to generalizations of various classical coloring results, including the theorems of Brooks, of Gallai, and of Erdős, Rubin and Taylor. Our main result is a DP-version of a theorem about partitions of graphs into a fixed number of induced subgraphs with bounded variable degeneracy due to Borodin, Kostochka, and Toft. Y1 - 2025 U6 - https://doi.org/10.1016/j.disc.2022.113186 SN - 0012-365X VL - 346 IS - 11 PB - Elsevier BV ER - TY - JOUR A1 - von Postel, Justus A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Point partition numbers: Decomposable and indecomposable critical graphs JF - Discrete Mathematics N2 - In the present paper we extend the following three coloring concepts for the class of finite undirected graphs having multiple edges but no loops. First of all, the generalized coloring concept, in which the same colored vertices of a graph induce a subgraph satisfying a prescribed graph property. Secondly, the concept of variable degeneracy, which was introduced by Borodin, Kostochka and Toft in 2000; this makes it possible to give a common generalization of the point partition number and the list chromatic number. Finally, the DP-coloring concept as introduced by Ďvorák and Postle in 2018, where a list assignment of a graph is replaced by a cover. Combining these three coloring concepts leads to generalizations of various classical coloring results, including the theorems of Brooks, of Gallai, and of Erdős, Rubin and Taylor. Our main result is a DP-version of a theorem about partitions of graphs into a fixed number of induced subgraphs with bounded variable degeneracy due to Borodin, Kostochka, and Toft. Y1 - 2025 U6 - https://doi.org/10.1016/j.disc.2022.112903 SN - 0012-365X VL - 345 IS - 8 PB - Elsevier BV ER - TY - JOUR A1 - von Postel, Justus A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Point Partition Numbers: Perfect Graphs JF - Graphs and Combinatorics Y1 - 2025 U6 - https://doi.org/10.1007/s00373-021-02410-w SN - 0911-0119 VL - 38 IS - 2 PB - Springer Science and Business Media LLC ER - TY - JOUR A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Partitions of hypergraphs under variable degeneracy constraints JF - Journal of Graph Theory N2 - The paper deals with partitions of hypergraphs into induced subhypergraphs satisfying constraints on their degeneracy. Our hypergraphs may have multiple edges, but no loops. Given a hypergraph and a sequence of vertex functions such that for all , we want to find a sequence of vertex disjoint induced subhypergraphs containing all vertices of such that each hypergraph is strictly ‐degenerate, that is, for every nonempty subhypergraph there is a vertex such that . Our main result in this paper says that such a sequence of hypergraphs exists if and only if is not a so‐called hard pair. Hard pairs form a recursively defined family of configurations, obtained from three basic types of configurations by the operation of merging a vertex. Our main result has several interesting applications related to generalized hypergraph coloring problems. Y1 - 2025 U6 - https://doi.org/https://doi.org/10.1002/jgt.22575 SN - 0364-9024 VL - 96 IS - 1 SP - 7 EP - 33 PB - Wiley ER - TY - JOUR A1 - Bang-Jensen, Jørgen A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Digraphs and Variable Degeneracy JF - SIAM Journal on Discrete Mathematics Y1 - 2025 U6 - https://doi.org/10.1137/20M1386827 SN - 0895-4801 VL - 36 IS - 1 SP - 578 EP - 595 PB - Society for Industrial & Applied Mathematics (SIAM) ER - TY - JOUR A1 - Schweser, Thomas T1 - Generalized hypergraph coloring JF - Discussiones Mathematicae Graph Theory Y1 - 2025 U6 - https://doi.org/10.7151/dmgt.2168 VL - 41 IS - 1 SP - 103 EP - 121 ER - TY - JOUR A1 - Schweser, Thomas T1 - DP-degree colorable hypergraphs JF - Theoretical Computer Science Y1 - 2025 U6 - https://doi.org/10.1016/j.tcs.2019.09.010 SN - 0304-3975 VL - 796 SP - 196 EP - 206 PB - Elsevier BV ER - TY - JOUR A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Partitions of multigraphs under minimum degree constraints JF - Discrete Applied Mathematics Y1 - 2025 U6 - https://doi.org/10.1016/j.dam.2018.10.016 SN - 0166-218X VL - 257 SP - 269 EP - 275 PB - Elsevier BV ER - TY - JOUR A1 - Schweser, Thomas A1 - Stiebitz, Michael T1 - Degree choosable signed graphs JF - Discrete Mathematics Y1 - 2025 U6 - https://doi.org/10.1016/j.disc.2017.01.007 SN - 0012-365X VL - 340 IS - 5 SP - 882 EP - 891 PB - Elsevier BV ER - TY - BOOK A1 - Stiebitz, Michael A1 - Schweser, Thomas A1 - Toft, Bjarne T1 - Brooks' Theorem BT - Graph Coloring and Critical Graphs T3 - Springer Monographs in Mathematics Y1 - 2025 SN - 9783031500640 U6 - https://doi.org/10.1007/978-3-031-50065-7 PB - Springer Nature Switzerland ER - TY - GEN A1 - Kläbe, Steffen A1 - Hagedorn, Stefan A1 - Gropengießer, Francis A1 - Schweser, Thomas T1 - Beyond the Data Warehouse: Modern and fast Data Analytics in Actian Vector. T2 - Datenbanksysteme für Business, Technologie und Web (BTW 2025) N2 - Modern data analytics cover a wide range of tools and frameworks besides traditional SQL-based analytics, leading to the need to transform traditional data warehouse solutions into data platforms. In this paper we focus on ecosystem integration, query performance and ease-of-use as key differentiators. We spotlight capabilities we introduced into our analytical database system Actian Vector with respect to these differentiators and highlight challenges we faced when applying research ideas to a production-ready system. The described capabilities cover ecosystem integrations with Apache Spark and a containerized services framework, cost model optimizations for robust query planning and several features to improve usability and manageability of the system. Y1 - 2025 U6 - https://doi.org/10.18420/BTW2025-35 SP - 691 EP - 697 ER -