IA Scholar Query: Fixpoint Alternation and the Game Quantifier.
https://scholar.archive.org/
Internet Archive Scholar query results feedeninfo@archive.orgWed, 03 Aug 2022 00:00:00 GMTfatcat-scholarhttps://scholar.archive.org/help1440To Be Announced
https://scholar.archive.org/work/73k2wsalfnei5kphsdyhtafgj4
In this survey we review dynamic epistemic logics with modalities for quantification over information change. Of such logics we present complete axiomatizations, focussing on axioms involving the interaction between knowledge and such quantifiers, we report on their relative expressivity, on decidability and on the complexity of model checking and satisfiability, and on applications. We focus on open problems and new directions for research.Hans van Ditmarschwork_73k2wsalfnei5kphsdyhtafgj4Wed, 03 Aug 2022 00:00:00 GMTThe amazing mixed polynomial closure and its applications to two-variable first-order logic
https://scholar.archive.org/work/lsaoylupergkvng77ju3vtr2yu
Polynomial closure is a standard operator which is applied to a class of regular languages. In this paper, we investigate three restrictions called left (LPol), right (RPol) and mixed polynomial closure (MPol). The first two were known while MPol is new. We look at two decision problems that are defined for every class C . Membership takes a regular language as input and asks if it belongs to C . Separation takes two regular languages as input and asks if there exists a third language in C including the first one and disjoint from the second. We prove that LPol, RPol and MPol preserve the decidability of membership under mild hypotheses on the input class, and the decidability of separation under much stronger hypotheses. We apply these results to natural hierarchies. First, we look at several language theoretic hierarchies that are built by applying LPol, RPol and MPol recursively to a single input class. We prove that these hierarchies can actually be defined using almost exclusively MPol. We also consider quantifier alternation hierarchies for two-variable first-order logic (FO 2 ) and prove that one can climb them using MPol. The result is generic in the sense that it holds for most standard choices of signatures. We use it to prove that for most of these choices, membership is decidable for all levels in the hierarchy. Finally, we prove that separation is decidable for the hierarchy of two-variable first-order logic equipped with only the linear order (FO 2 (<)).Thomas Placework_lsaoylupergkvng77ju3vtr2yuTue, 02 Aug 2022 00:00:00 GMTOptimistic and Topological Value Iteration for Simple Stochastic Games
https://scholar.archive.org/work/36dsha6imzbxbk7sbe65jkq4ue
While value iteration (VI) is a standard solution approach to simple stochastic games (SSGs), it suffered from the lack of a stopping criterion. Recently, several solutions have appeared, among them also "optimistic" VI (OVI). However, OVI is applicable only to one-player SSGs with no end components. We lift these two assumptions, making it available to general SSGs. Further, we utilize the idea in the context of topological VI, where we provide an efficient precise solution. In order to compare the new algorithms with the state of the art, we use not only the standard benchmarks, but we also design a random generator of SSGs, which can be biased towards various types of models, aiding in understanding the advantages of different algorithms on SSGs.Muqsit Azeem, Alexandros Evangelidis, Jan Křetínský, Alexander Slivinskiy, Maximilian Weiningerwork_36dsha6imzbxbk7sbe65jkq4ueFri, 29 Jul 2022 00:00:00 GMTFast Symbolic Algorithms for Omega-Regular Games under Strong Transition Fairness
https://scholar.archive.org/work/3tsi7msp5verla6db2bdhiacpe
We consider fixpoint algorithms for two-player games on graphs with ω-regular winning conditions, where the environment is constrained by a strong transition fairness assumption. Strong transition fairness is a widely occurring special case of strong fairness, which requires that any execution is strongly fair with respect to a specified set of live edges: whenever the source vertex of a live edge is visited infinitely often along a play, the edge itself is traversed infinitely often along the play as well. We show that, surprisingly, strong transition fairness retains the algorithmic characteristics of the fixpoint algorithms for ω-regular games – the new algorithms have the same alternation depth as the classical algorithms but invoke a new type of predecessor operator. For Rabin games with k pairs, the complexity of the new algorithm is O(n^k+2k!) symbolic steps, which is independent of the number of live edges in the strong transition fairness assumption. Further, we show that GR(1) specifications with strong transition fairness assumptions can be solved with a 3-nested fixpoint algorithm, same as the usual algorithm. In contrast, strong fairness necessarily requires increasing the alternation depth depending on the number of fairness assumptions. We get symbolic algorithms for (generalized) Rabin, parity and GR(1) objectives under strong transition fairness assumptions as well as a direct symbolic algorithm for qualitative winning in stochastic ω-regular games that runs in O(n^k+2k!) symbolic steps, improving the state of the art. Finally, we have implemented a BDD-based synthesis engine based on our algorithm. We show on a set of synthetic and real benchmarks that our algorithm is scalable, parallelizable, and outperforms previous algorithms by orders of magnitude.Tamajit Banerjee, Rupak Majumdar, Kaushik Mallik, Anne-Kathrin Schmuck, Sadegh Soudjaniwork_3tsi7msp5verla6db2bdhiacpeFri, 29 Jul 2022 00:00:00 GMTOn the connection of probabilistic model checking, planning, and learning for system verification
https://scholar.archive.org/work/elsht7dndnf7jlue3wo3zte7l4
This thesis presents approaches using techniques from the model checking, planning, and learning community to make systems more reliable and perspicuous. First, two heuristic search and dynamic programming algorithms are adapted to be able to check extremal reachability probabilities, expected accumulated rewards, and their bounded versions, on general Markov decision processes (MDPs). Thereby, the problem space originally solvable by these algorithms is enlarged considerably. Correctness and optimality proofs for the adapted algorithms are given, and in a comprehensive case study on established benchmarks it is shown that the implementation, called Modysh, is competitive with state-of-the-art model checkers and even outperforms them on very large state spaces. Second, Deep Statistical Model Checking (DSMC) is introduced, usable for quality assessment and learning pipeline analysis of systems incorporating trained decision-making agents, like neural networks (NNs). The idea of DSMC is to use statistical model checking to assess NNs resolving nondeterminism in systems modeled as MDPs. The versatility of DSMC is exemplified in a number of case studies on Racetrack, an MDP benchmark designed for this purpose, flexibly modeling the autonomous driving challenge. In a comprehensive scalability study it is demonstrated that DSMC is a lightweight technique tackling the complexity of NN analysis in combination with the state space explosion problem. III Zusammenfassung Diese Arbeit präsentiert Ansätze, die Techniken aus dem Model Checking, Planning und Learning Bereich verwenden, um Systeme verlässlicher und klarer verständlich zu machen. Zuerst werden zwei Algorithmen für heuristische Suche und dynamisches Programmieren angepasst, um Extremwerte für Erreichbarkeitswahrscheinlichkeiten, Erwartungswerte für Kosten und beschränkte Varianten davon, auf generellen Markov Entscheidungsprozessen (MDPs) zu untersuchen. Damit wird der Problemraum, der ursprünglich mit diesen Algorithmen gelöst wurde, deutlich erweitert. Korrektheits-und Optimalitätsbeweise für die angepassten Algorithmen werden gegeben und in einer umfassenden Fallstudie wird gezeigt, dass die Implementierung, namens Modysh, konkurrenzfähig mit den modernsten Model Checkern ist und deren Leistung auf sehr großen Zustandsräumen sogar übertrifft. Als Zweites wird Deep Statistical Model Checking (DSMC) für die Qualitätsbewertung und Lernanalyse von Systemen mit integrierten trainierten Entscheidungsgenten, wie z.B. neuronalen Netzen (NN), eingeführt. Die Idee von DSMC ist es, statistisches Model Checking zur Bewertung von NNs zu nutzen, die Nichtdeterminismus in Systemen, die als MDPs modelliert sind, auflösen. Die Vielseitigkeit des Ansatzes wird in mehreren Fallbeispielen auf Racetrack gezeigt, einer MDP Benchmark, die zu diesem Zweck entwickelt wurde und die Herausforderung des autonomen Fahrens flexibel modelliert. In einer umfassenden Skalierbarkeitsstudie wird demonstriert, dass DSMC eine leichtgewichtige Technik ist, die die Komplexität der NN-Analyse in Kombination mit dem State Space Explosion Problem bewältigt. V Some Personal Words My endeavor of pursuing a PhD at the Dependable Systems and Software chair started already in August 2017 before even signing a contract. After several tutor positions and a lot of fun and work in the mathematics preparatory course team, I already knew Felix, Gereon, and Sebastian who promised me that working here would be a lot of fun. To get to know also the others in the team, Holger offered me the opportunity to take part in the chair's retreat in Tanna, a very small city in Thüringen. Nobody expected that this trip would turn into a literal crash landing for me. But after surviving this first shock, returning home without getting lost at a toilet on a service station, and knowing that Vahid has a big heart for goats, I started officially in November and shared my office with Gilles and Yuliya. Dear Gilles, I have to confess, that at first glance I was misled like the grandma who changed to the other side of the street but very soon we turned into office mates who know the habits of each other very well. We had quite some philosophical and deep discussions about our work and doing a PhD in general. All this helped me so much in overcoming some doubts and I learned a lot from you. Thank you very much! Soon we established Game and Movie Nights in our new leisure room with the very extravagant orange zebra sofa which is exactly 1 m(ichaela) long. At CONFESTA 2018 I got the chance to go with Daniel, Gereon, and Sebastian on the greatest trip ever. We visited Beijing for the conference and the final CAP workshop. We made it without getting hacked, or thrown into prison, but with hurting legs from all the sightseeing, climbing up the wall, and especially from the soccer match Gereon, Rob van Glabbeek, Uwe Nestmann, and me won against Kim Larsen.Michaela Klauck, Universität Des Saarlandeswork_elsht7dndnf7jlue3wo3zte7l4Mon, 18 Jul 2022 00:00:00 GMTA Stochastic Game Approach to Masking Fault-Tolerance: Bisimulation and Quantification
https://scholar.archive.org/work/eozdezedubab3nfddswmvepoti
We introduce a formal notion of masking fault-tolerance between probabilistic transition systems based on a variant of probabilistic bisimulation (named masking simulation). We also provide the corresponding probabilistic game characterization. Even though these games could be infinite, we propose a symbolic way of representing them, such that it can be decided in polynomial time if there is a masking simulation between two probabilistic transition systems. We use this notion of masking to quantify the level of masking fault-tolerance exhibited by almost-sure failing systems, i.e., those systems that eventually fail with probability 1. The level of masking fault-tolerance of almost-sure failing systems can be calculated by solving a collection of functional equations. We produce this metric in a setting in which the minimizing player behaves in a strong fair way (mimicking the idea of fair environments), and limit our study to memoryless strategies due to the infinite nature of the game. We implemented these ideas in a prototype tool, and performed an experimental evaluation.Pablo F. Castro, Pedro D'Argenio, Luciano Putruele, Ramiro Demasiwork_eozdezedubab3nfddswmvepotiTue, 05 Jul 2022 00:00:00 GMTStrongly First Order, Domain Independent Dependencies: the Union-Closed Case
https://scholar.archive.org/work/o7povnhctndapkj5ilukw73ft4
Team Semantics generalizes Tarski's Semantics by defining satisfaction with respect to sets of assignments rather than with respect to single assignments. Because of this, it is possible to use Team Semantics to extend First Order Logic via new kinds of connectives or atoms - most importantly, via dependency atoms that express dependencies between different assignments. Some of these extensions are more expressive than First Order Logic proper, while others are reducible to it. In this work, I provide necessary and sufficient conditions for a dependency atom that is domain independent (in the sense that its truth or falsity in a relation does not depend on the existence in the model of elements that do not occur in the relation) and union closed (in the sense that whenever it is satisfied by all members of a family of relations it is also satisfied by their union) to be strongly first order, in the sense that the logic obtained by adding them to First Order Logic is no more expressive than First Order Logic itself.Pietro Gallianiwork_o7povnhctndapkj5ilukw73ft4Thu, 30 Jun 2022 00:00:00 GMTCohomology in Constraint Satisfaction and Structure Isomorphism
https://scholar.archive.org/work/3e7gfqwegnfrfnivwf7r5ei2sy
Constraint satisfaction (CSP) and structure isomorphism (SI) are among the most well-studied computational problems in Computer Science. While neither problem is thought to be in , much work is done on approximations to both problems. Two such historically important approximations are the k-consistency algorithm for CSP and the k-Weisfeiler-Leman algorithm for SI, both of which are based on propagating local partial solutions. The limitations of these algorithms are well-known; k-consistency can solve precisely those CSPs of bounded width and k-Weisfeiler-Leman can only distinguish structures which differ on properties definable in C^k. In this paper, we introduce a novel sheaf-theoretic approach to CSP and SI and their approximations. We show that both problems can be viewed as deciding the existence of global sections of presheaves, ℋ_k(A,B) and ℐ_k(A,B) and that the success of the k-consistency and k-Weisfeiler-Leman algorithms correspond to the existence of certain efficiently computable subpresheaves of these. Furthermore, building on work of Abramsky and others in quantum foundations, we show how to use Čech cohomology in ℋ_k(A,B) and ℐ_k(A,B) to detect obstructions to the existence of the desired global sections and derive new efficient cohomological algorithms extending k-consistency and k-Weisfeiler-Leman. We show that cohomological k-consistency can solve systems of equations over all finite rings and that cohomological Weisfeiler-Leman can distinguish positive and negative instances of the Cai-Fürer-Immerman property over several important classes of structures.Adam Ó Conghailework_3e7gfqwegnfrfnivwf7r5ei2syThu, 30 Jun 2022 00:00:00 GMTStrategy Synthesis for Global Window PCTL
https://scholar.archive.org/work/l3olzjwmtjdila2yp7d53dhrkm
Given a Markov decision process (MDP) M and a formula Φ, the strategy synthesis problem asks if there exists a strategy σ s.t. the resulting Markov chain M[σ] satisfies Φ. This problem is known to be undecidable for the probabilistic temporal logic PCTL. We study a class of formulae that can be seen as a fragment of PCTL where a local, bounded horizon property is enforced all along an execution. Moreover, we allow for linear expressions in the probabilistic inequalities. This logic is at the frontier of decidability, depending on the type of strategies considered. In particular, strategy synthesis is decidable when strategies are deterministic while the general problem is undecidable.Benjamin Bordais, Damien Busatto-Gaston, Shibashis Guha, Jean-François Raskin, Mikołaj Bojańczyk, Emanuela Merelli, David P. Woodruffwork_l3olzjwmtjdila2yp7d53dhrkmTue, 28 Jun 2022 00:00:00 GMTNotes on presheaf representations of strategies and cohomological refinements of k-consistency and k-equivalence
https://scholar.archive.org/work/xlapiakygbbxhbnwkki2yrkkzq
In this note, we show how positional strategies for k-pebble games have a natural representation as certain presheaves. These representations correspond exactly to the sheaf-theoretic models of contextuality introduced by Abramsky-Brandenburger. We study the notion of cohomological k-consistency recently introduced by Adam O' Conghaile from this perspective.Samson Abramskywork_xlapiakygbbxhbnwkki2yrkkzqFri, 24 Jun 2022 00:00:00 GMTLow-Level Bi-Abduction
https://scholar.archive.org/work/y2ffm5gxmzfw7j3wprkjly3ata
The paper proposes a new static analysis designed to handle open programs, i.e., fragments of programs, with dynamic pointer-linked data structures - in particular, various kinds of lists - that employ advanced low-level pointer operations. The goal is to allow such programs be analysed without a need of writing analysis harnesses that would first initialise the structures being handled. The approach builds on a special flavour of separation logic and the approach of bi-abduction. The code of interest is analyzed along the call tree, starting from its leaves, with each function analysed just once without any call context, leading to a set of contracts summarizing the behaviour of the analysed functions. In order to handle the considered programs, methods of abduction existing in the literature are significantly modified and extended in the paper. The proposed approach has been implemented in a tool prototype and successfully evaluated on not large but complex programs.Lukáš Holík, Petr Peringer, Adam Rogalewicz, Veronika Šoková, Tomáš Vojnar, Florian Zuleger, Karim Ali, Jan Vitekwork_y2ffm5gxmzfw7j3wprkjly3ataThu, 23 Jun 2022 00:00:00 GMTSoftware Verification of Hyperproperties Beyond k-Safety
https://scholar.archive.org/work/qihmnswinjaixpdijrtgr7sl3u
Temporal hyperproperties are system properties that relate multiple execution traces. For (finite-state) hardware, temporal hyperproperties are supported by model checking algorithms, and tools for general temporal logics like HyperLTL exist. For (infinite-state) software, the analysis of temporal hyperproperties has, so far, been limited to k-safety properties, i.e., properties that stipulate the absence of a bad interaction between any k traces. In this paper, we present an automated method for the verification of ∀^k∃^l-safety properties in infinite-state systems. A ∀^k∃^l-safety property stipulates that for any k traces, there exist l traces such that the resulting k+l traces do not interact badly. This combination of universal and existential quantification allows us to express many properties beyond k-safety, including, for example, generalized non-interference or program refinement. Our method is based on a strategy-based instantiation of existential trace quantification combined with a program reduction, both in the context of a fixed predicate abstraction. Importantly, our framework allows for mutual dependence of strategy and reduction.Raven Beutner, Bernd Finkbeinerwork_qihmnswinjaixpdijrtgr7sl3uTue, 07 Jun 2022 00:00:00 GMTSound Cross-Contract Reachability Analysis of Ethereum Smart Contracts
https://scholar.archive.org/work/dhkqd5g42nc37avr5a2tzfieoa
Die Ethereum-Blockchain ist die bekannteste Plattform, die die Ausführung von Smart Contracts im Zuge von Transaktionen ermöglicht. Ein Smart Contract ist ein Programm, welches beschreibt, wie der durch die Blockchain geführte Zustand angepasst werden soll. Im Rahmen seiner Ausführung kann ein Smart Contract auch andere Contracts aufrufen oder erzeugen. Fehler in der Implementierung eines Smart Contracts können zu einem inkonsistenten oder unerwarteten Zustand des Smart Contracts führen, was katastrophale finanzielle Konsequenzen haben kann. Wir präsentieren daher multeThor, ein Tool zur statischen Analyse, welches in der Lage ist, Abfragen bezüglich der Erreichbarkeit bestimmter Ausführungszustände von Smart Contracts zu beantworten. Um mit statisch unbekannter Information umgehen zu können, nutzen wir Techniken der abstrakten Interpretation. Die Implementierung der Analyse nutzt dann eine abstrakte Variante der Bytecode-Semantik von Ethereum Smart Contracts, die durch Resolution von Horn-Klauseln automatisch ausgeführt werden kann. Während einer Präanalyse versucht das Tool, andere Contracts, die aufgerufen werden können, konkret zu bestimmen. Danach wird der Bytecode solcher Aufrufziele automatisch heruntergeladen und schlussendlich in späteren Phasen der Analyse eingebunden. Das erlaubt es, die Effekte von Aufrufen bekannter Contracts präziser zu bestimmen, und ermöglicht im Besonderen eine brauchbare Analyse von Contracts mit Bibliotheksaufrufen. Eine wesentliche Eigenschaft von multeThor ist dessen Korrektheit, womit gemeint ist, dass das Tool stets eine Abstraktion eines erreichbaren Ausführungszustands ableitet. Dadurch kann multeThor genutzt werden, um die Abwesenheit problematischer Ausführungszustände zu beweisen. Wir legen eine Beweisskizze vor, um die Korrektheit von multeThor formal zu zeigen. Mittels einer experimentellen Evaluierung, basierend auf einem aus Contracts der Ethereum-Blockchain bestehenden Datensatz, demonstrieren wir, dass multeThor genutzt werden kann, um die generische Sicherheitse [...]Martin Schweighofer, Matteo Maffei, Markus Schererwork_dhkqd5g42nc37avr5a2tzfieoaWed, 01 Jun 2022 00:00:00 GMTThe Reactive Synthesis Competition (SYNTCOMP): 2018-2021
https://scholar.archive.org/work/dl2crkokcnbwbogzxj2v27w73a
We report on the last four editions of the reactive synthesis competition (SYNTCOMP 2018-2021). We briefly describe the evaluation scheme and the experimental setup of SYNTCOMP. Then, we introduce new benchmark classes that have been added to the SYNTCOMP library and give an overview of the participants of SYNTCOMP. Finally, we present and analyze the results of our experimental evaluations, including a ranking of tools with respect to quantity and quality of solutions.Swen Jacobs, Guillermo A. Perez, Remco Abraham, Veronique Bruyere, Michael Cadilhac, Maximilien Colange, Charly Delfosse, Tom van Dijk, Alexandre Duret-Lutz, Peter Faymonville, Bernd Finkbeiner, Ayrat Khalimov, Felix Klein, Michael Luttenberger, Klara Meyer, Thibaud Michaud, Adrien Pommellet, Florian Renkin, Philipp Schlehuber-Caissier, Mouhammad Sakr, Salomon Sickert, Gaetan Staquet, Clement Tamines, Leander Tentrup, Adam Walkerwork_dl2crkokcnbwbogzxj2v27w73aWed, 01 Jun 2022 00:00:00 GMTWhen Can We Answer Queries Using Result-Bounded Data Interfaces?
https://scholar.archive.org/work/2swct5duffb75avfokkv4q7hle
We consider answering queries on data available through access methods, that provide lookup access to the tuples matching a given binding. Such interfaces are common on the Web; further, they often have bounds on how many results they can return, e.g., because of pagination or rate limits. We thus study result-bounded methods, which may return only a limited number of tuples. We study how to decide if a query is answerable using result-bounded methods, i.e., how to compute a plan that returns all answers to the query using the methods, assuming that the underlying data satisfies some integrity constraints. We first show how to reduce answerability to a query containment problem with constraints. Second, we show "schema simplification" theorems describing when and how result-bounded services can be used. Finally, we use these theorems to give decidability and complexity results about answerability for common constraint classes.Antoine Amarilli, Michael Benediktwork_2swct5duffb75avfokkv4q7hleWed, 01 Jun 2022 00:00:00 GMTParallel Contests for Crowdsourcing Reviews: Existence and Quality of Equilibria
https://scholar.archive.org/work/s44gwucokbbsjbhwmpijrxcwam
Motivated by the intricacies of allocating treasury funds in blockchain settings, we study the problem of crowdsourcing reviews for many different proposals, in parallel. During the reviewing phase, every reviewer can select the proposals to write reviews for, as well as the quality of each review. The quality levels follow certain very coarse community guidelines and can have values such as 'excellent' or 'good'. Based on these scores and the distribution of reviews, every reviewer will receive some reward for their efforts. In this paper, we design a reward scheme and show that it always has pure Nash equilibria, for any set of proposals and reviewers. In addition, we show that these equilibria guarantee constant factor approximations for two natural metrics: the total quality of all reviews, as well as the fraction of proposals that received at least one review, compared to the optimal outcome.Georgios Birmpas, Lyudmila Kovalchuk, Philip Lazos, Roman Oliynykovwork_s44gwucokbbsjbhwmpijrxcwamWed, 25 May 2022 00:00:00 GMTOASIcs, Volume 99, AIB 2022, Complete Volume
https://scholar.archive.org/work/bwook3qzlnh4rcdq3po2nchqpe
OASIcs, Volume 99, AIB 2022, Complete VolumeCamille Bourgaux, Ana Ozaki, Rafael Peñalozawork_bwook3qzlnh4rcdq3po2nchqpeWed, 25 May 2022 00:00:00 GMTThe amazing mixed polynomial closure and its applications to two-variable first-order logic
https://scholar.archive.org/work/yy3wh5zmavfrxenwq65ukeixeu
Polynomial closure is a standard operator which is applied to a class of regular languages. In the paper, we investigate three restrictions called left (LPol), right (RPol) and mixed polynomial closure (MPol). The first two were known while MPol is new. We look at two decision problems that are defined for every class C. Membership takes a regular language as input and asks if it belongs to C. Separation takes two regular languages as input and asks if there exists a third language in C including the first one and disjoint from the second. We prove that LPol, RPol and MPol preserve the decidability of membership under mild hypotheses on the input class, and the decidability of separation under much stronger hypotheses. We apply these results to natural hierarchies. First, we look at several language theoretic hierarchies that are built by applying LPol, RPol and MPol recursively to a single input class. We prove that these hierarchies can actually be defined using almost exclusively MPol. We also consider quantifier alternation hierarchies for two-variable first-order logic and prove that one can climb them using MPol. The result is generic in the sense that it holds for most standard choices of signatures. We use it to prove that for most of these choices, membership is decidable for all levels in the hierarchy. Finally, we prove that separation is decidable for the hierarchy of two-variable first-order logic equipped with only the linear order.Thomas Placework_yy3wh5zmavfrxenwq65ukeixeuMon, 23 May 2022 00:00:00 GMTProceedings of the 2022 Joint Workshop of the German Research Training Groups in Computer Science
https://scholar.archive.org/work/lvykkw5kcfhlvolc6paa2sxczu
Having spent two successive years running online to prevent the spread of the Corona virus, the traditional annual meeting of the German Research Training Groups (RTGs) funded by the Deutsche Forschungsgemeinschaft (DFG) in the field of computer science returns to Schloss Dagstuhl --– Leibniz Center for Informatics, one of the world's premier venues for computer science-related seminars. Returning to Dagstuhl and hosting this meeting as an in-person-only event was a deliberate decision to revive interaction modes that many of the funded researchers had yet to experience: fostering personal interchange of ideas and experiences in order to strengthen the connection within the German computer science community. This volume documents the abstracts of the research topics of funded researchers in the participating RTGs. The event was jointly organized by RTG 2475 (Cybercrime and Forensic Computing) and RTG 2428 (ConVeY --- Continuous Verification of Cyber-Physical Systems). It took place between Sunday, June 12 and Wednesday, June 15, 2022, as in-person only Dagstuhl Event 22243. The meeting featured the usual sequence of research presentations by funded researchers, networking meetings for PIs and RTG coordinators, as well as two invited talks, one by Professor Martina Seidl (JKU Linz, Austria) on "Competitions as Scientific Method" and another by Professor Jennifer Byrne (School of Medical Sciences, The University of Sydney, Australia) titled "An introduction to research paper mills". Because last year's event marked the 25th anniversary of the workshop series, it featured a live interview with Professor Otto Spaniol who had initiated the workshop series in 1996. We document the interview in this volume.Felix Freiling, Helmut Seidl, 2022 2022 Joint Workshop Of The German Research Training Groups In Computer Science June 12–June 15work_lvykkw5kcfhlvolc6paa2sxczuTue, 17 May 2022 00:00:00 GMTA tetrachotomy of ontology-mediated queries with a covering axiom
https://scholar.archive.org/work/yfzmmcszw5ggzivkhdlobd7dpu
Our concern is the problem of efficiently determining the data complexity of answering queries mediated by description logic ontologies and constructing their optimal rewritings to standard database queries. Originated in ontology-based data access and datalog optimisation, this problem is known to be computationally very complex in general, with no explicit syntactic characterisations available. In this article, aiming to understand the fundamental roots of this difficulty, we strip the problem to the bare bones and focus on Boolean conjunctive queries mediated by a simple covering axiom stating that one class is covered by the union of two other classes. We show that, on the one hand, these rudimentary ontology-mediated queries, called disjunctive sirups (or d-sirups), capture many features and difficulties of the general case. For example, answering d-sirups is Pi^p_2-complete for combined complexity and can be in AC0 or LogSpace-, NL-, P-, or coNP-complete for data complexity (with the problem of recognising FO-rewritability of d-sirups being 2ExpTime-hard); some d-sirups only have exponential-size resolution proofs, some only double-exponential-size positive existential FO-rewritings and single-exponential-size nonrecursive datalog rewritings. On the other hand, we prove a few partial sufficient and necessary conditions of FO- and (symmetric/linear-) datalog rewritability of d-sirups. Our main technical result is a complete and transparent syntactic AC0/NL/P/coNP tetrachotomy of d-sirups with disjoint covering classes and a path-shaped Boolean conjunctive query. To obtain this tetrachotomy, we develop new techniques for establishing P- and coNP-hardness of answering non-Horn ontology-mediated queries as well as showing that they can be answered in NL.Olga Gerasimova, Stanislav Kikot, Agi Kurucz, Vladimir Podolskii, Michael Zakharyaschevwork_yfzmmcszw5ggzivkhdlobd7dpuThu, 05 May 2022 00:00:00 GMT