September 2022 - informatik-vortraege

Einladung: Informatik-Oberseminar Tim Hartmann
by Tim Hartmann 26 Sep '22

26 Sep '22

+********************************************************************** * * * Einladung * * * * Informatik-Oberseminar * * * +********************************************************************** Zeit: Donnerstag, 6. Oktober 2022, 15:00 Uhr Ort: Raum 9222, Ahornstr. 55 Referent: Tim Hartmann M.Sc. Lehrstuhl Informatik 1 Thema: Facility Location on Graphs Abstract: We study two closely related Facility Location problems on graphs where all edges have unit length and where the facilities may also be positioned in the interior of the edges. For delta-Dispersion the goal is to position as many facilities as possible subject to the condition that any two facilities have at least distance delta from each other. For delta-Covering the goal is to cover the entire graph with the minimum number of facilities; that is, we want to position as few facilities as possible subject to the condition that every point on every edge is at distance at most delta from one of these facilities. We investigate the algorithmic complexity of these problems for every real distance value delta. Further, we explore the complexity of these problems with the solution size as parameter. Finally, we study delta-Dispersion with parameters that measure the complexity of the input graph, such as treewidth, treedepth and neighborhood diversity. Es laden ein: die Dozentinnen und Dozenten der Informatik

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[Informatik-assistenten] Einladung: Informatik-Oberseminar Rebecca
by Rebecca Haehn 20 Sep '22

20 Sep '22

+********************************************************************** * * * Einladung * * * * Informatik-Oberseminar * * * +********************************************************************** Zeit: Freitag, 21. Oktober 2022, 14:30 Uhr Ort: Raum 9U10 (2359|0.10), E3, Informatikzentrum, Ahornstr. 55 Referent: Rebecca Haehn M.Sc. (Theory of Hybrid Systems) Thema: Optimisation and Analysis of Railway Timetables under Consideration of Uncertainties Abstract: Railway systems are complex systems that are strongly affected by uncertainties like weather, technical problems, or demand. Despite these uncertainties, railway systems need to function efficiently. In general this thesis aims to advance the consideration of uncertainty in the railway planning process to optimally utilise the existing railway network capacity. The focus in this thesis is on the delays that result from the uncertain environmental conditions. To consider these in the railway planning process, a symbolic simulation algorithm is proposed to examine the delay propagation in a railway network for a given timetable. This allows to estimate the timetable robustness and the network capacity. Several performance indicators for railway timetables that can be evaluated using the symbolic simulation are discussed. To optimally utilise the network capacity also an algorithm to schedule additional freight trains is presented. The main contributions of this thesis are the following: - An algorithm to schedule additional freight trains is presented, to utilise the remaining network capacity without disturbing an existing timetable. - A novel symbolic simulation algorithm for railway timetables is proposed. The algorithm receives as input a railway infrastructure model, a corresponding timetable, and discrete primary delay dis- tributions. It computes iteratively over time the delay propagation in the given railway system. Symbolic expressions are used to represent multiple possible values for the primary delays. This enables to simulate all discrete primary delay combinations at once. - An implementation of these algorithms is provided in C++ and evaluated on some real-world railway infrastructure networks and timetables based on the German railway system. The applicability and functionality of the algorithms is demonstrated. The proposed symbolic simulation algorithm is aimed to be a helpful addition to existing railway timetable simulations, which are mostly based on Monte Carlo simulation. In contrast to those, the symbolic approach stores the history of specific train states, which can be used to explain the occurring delays. In addition, the results of the symbolic simulation are exact with respect to the input model and the discrete primary delay distributions. Es laden ein: die Dozentinnen und Dozenten der Informatik

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[sekretariate] Einladung: Informatik-Oberseminar Shahid Khan
by Elke Ohlenforst 19 Sep '22

19 Sep '22

+********************************************************************** * * * Einladung * * * * Informatik-Oberseminar * * * +********************************************************************** Zeit: Dienstag, 4. October 2022, 10:00 Uhr Ort: Raum 9222, Geb. E3, 2. Etage, Informatikzentrum, Ahornstr. 55 Referent: Shahid Khan M.Sc. (Lehrstuhl Informatik 2) Thema: Boolean-logic Driven Markov Processes - Explained. Analysed. Verified. Abstract: Model-based dependability studies of engineering systems amount to quantifying and improving dependability measures. These measures include reliability, availability, maintainability and safety. Two key ingredients of such studies are 1) models capturing the system behaviour to an acceptable level of abstraction and 2) efficient and accurate analysis techniques to quantify dependability measures. Among the modelling techniques, static (or standard) fault trees (SFTs) is a prominent dependability modelling language extensively used by engineers to develop system models. However, it lacks expressive power as it cannot model temporal dependencies of failures and has limited support for repairs. Boolean logic-driven Markov processes (BDMPs) and dynamic fault trees (DFTs) are two classical dynamic extensions of SFTs that aim to mitigate the expressive power limitation issue of SFTs. While DFTs are (generally) restricted to non-repairable systems, BDMPs natively support repairs. The BDMP language has a long-standing industrial usage history; the leading French electricity utility company (EDF) extensively uses BDMPs to conduct dependability studies. Among the analysis techniques, probabilistic model checking is a verification technique to determine the probability of a state-space model satisfying or refuting a logical property. It combines efficient, fully automated verification algorithms with numerical analysis. The results of these automated verification procedures are numeric values that dependability practitioners use to attain the reliability growth of their systems. The issue with BDMPs is that it lacks numerically exact analysis support and adequately documented semantics. EDF provides two analysis tools for BDMPs: 1) a Monte-Carlo simulator and 2) a sequence exploration tool. Both tools provide approximate results, which may not be acceptable for stringent dependability requirements of safet-criticalsystems. The semantics of BDMPs is essential for a comparative study with other modelling languages, e.g., DFTs. This dissertation, developed in collaboration with EDF, presents semantics and a model checker for BDMPs: -- we propose Markov automaton- and generalised stochastic Petri net-based semantics to BDMPs and empirically establish the accuracy, -- we develop a probabilistic model checker for BDMPs and enhance the scalability of the model checker using partial state-space exploration techniques, and -- we contrast BDMPs to DFTs and lift the repairable behaviour of BDMPs to repairable DFTs. This dissertation provides a holistic view of BDMPs. An exciting outcome of this dissertation is that our model checker can analyse the Markovian subset of the EDF-maintained Figaro language. This subset includes capacity analysis diagrams, dynamic reliability block diagrams, electric circuits, Petri nets, process diagrams, telecommunication networks, and other EDF-developed Figaro-based modelling formalisms. In this presentation, we provide: (1) a detailed introduction to the BDMP formalism, (2) an insight of the BDMP model checker, and (3) the semantics of BDMPs. Es laden ein: die Dozentinnen und Dozenten der Informatik

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Einladung: Informatik-Oberseminar Herr Thomas Osterland
by Leany Maaßen 05 Sep '22

05 Sep '22

+********************************************************************** * * * Einladung * * * * Informatik-Oberseminar * * * +********************************************************************** Zeit: Dienstag, 20.09.2022, 10:00-11:00 Uhr Der öffentliche Vortrag findet hybrid statt: Raum: Raum 5053.2 (B-IT-Hörsaal)/Informatikzentrum, Ahornstraße 55 Zoom: https://rwth.zoom.us/j/91824143381?pwd=dU5SNSt2TWtUMlZTOVFtRkczN1RvQT09 Meeting-ID: 918 2414 3381 Kenncode: 827047 Referent: Herr Thomas Osterland, M. Sc. Lehrstuhl Informatik 5 Thema: Distributed Ledger Technology Processes Abstract: DLT offers new means to establish trust relationships within cooperative processes among enterprises and thereby enables the implementation of use cases with a lack of existing intermediaries. Prominent examples of use cases are financial applications, provenance tracking and identity management. All of them are contingent upon trust in business processes and require the maintained security of the distributed ledger, that strongly depends on the heterogeneity and robustness of the underlying ecosystem. Participants need to trust the security of the ecosystem and the trust must be maintained over time. Therefore, the distributed ledger technology is not a simple component, that can be easily integrated into an existing application unless the complex relationship between participants and their trust into the underlying ecosystem is considered early in the engineering process. This thesis introduces a framework, that comprises a structured methodology and tooling as a means to support conventional software processes that allow software architects to address the specific requirements of distributed ledger applications. We argue that these subjects are important to ensure the quality and sustainability of an application, since 1) a distributed ledger, that is not capable of handling future requirements of a use case represents eventually a bottleneck and thus, harms the efficient and reliable execution of business processes, 2) smart contracts with software bugs, that either prevent the efficient execution of business processes or favor one party over another will erode the trust that participants have into the ecosystem, and 3) if the DLT is not capable of securing substantial amounts of data use cases, that rely on the processing of data are disadvantaged and the consequences for an ecosystem when handling large amounts of data in the future are unforeseeable. Es laden ein: die Dozentinnen und Dozenten der Informatik _______________________________ Leany Maaßen RWTH Aachen University Lehrstuhl Informatik 5, LuFG Informatik 5 Prof. Dr. Stefan Decker, Prof. Dr. Matthias Jarke, Prof. Gerhard Lakemeyer Ph.D. Ahornstrasse 55 D-52074 Aachen Tel: 0241-80-21509 Fax: 0241-80-22321 E-Mail: maassen(a)dbis.rwth-aachen.de

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