Reachability Problems: 8th International Workshop, RP 2014, Oxford, UK, September 22-24, 2014. Proceedings PDF
Preview Reachability Problems: 8th International Workshop, RP 2014, Oxford, UK, September 22-24, 2014. Proceedings
Joël Ouaknine Igor Potapov James Worrell (Eds.) 2 6 7 8 S C Reachability Problems N L 8th International Workshop, RP 2014 Oxford, UK, September 22–24, 2014 Proceedings 123 Lecture Notes in Computer Science 8762 CommencedPublicationin1973 FoundingandFormerSeriesEditors: GerhardGoos,JurisHartmanis,andJanvanLeeuwen EditorialBoard DavidHutchison LancasterUniversity,UK TakeoKanade CarnegieMellonUniversity,Pittsburgh,PA,USA JosefKittler UniversityofSurrey,Guildford,UK JonM.Kleinberg CornellUniversity,Ithaca,NY,USA AlfredKobsa UniversityofCalifornia,Irvine,CA,USA FriedemannMattern ETHZurich,Switzerland JohnC.Mitchell StanfordUniversity,CA,USA MoniNaor WeizmannInstituteofScience,Rehovot,Israel OscarNierstrasz UniversityofBern,Switzerland C.PanduRangan IndianInstituteofTechnology,Madras,India BernhardSteffen TUDortmundUniversity,Germany DemetriTerzopoulos UniversityofCalifornia,LosAngeles,CA,USA DougTygar UniversityofCalifornia,Berkeley,CA,USA GerhardWeikum MaxPlanckInstituteforInformatics,Saarbruecken,Germany Joël Ouaknine Igor Potapov James Worrell (Eds.) Reachability Problems 8th International Workshop, RP 2014 Oxford, UK, September 22-24, 2014 Proceedings 1 3 VolumeEditors JoëlOuaknine UniversityofOxford DepartmentofComputerScience Oxford,UK E-mail:[email protected] IgorPotapov UniversityofLiverpool DepartmentofComputerScience Liverpool,UK E-mail:[email protected] JamesWorrell UniversityofOxford DepartmentofComputerScience Oxford,UK E-mail:[email protected] ISSN0302-9743 e-ISSN1611-3349 ISBN978-3-319-11438-5 e-ISBN978-3-319-11439-2 DOI10.1007/978-3-319-11439-2 SpringerChamHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2014948071 LNCSSublibrary:SL1–TheoreticalComputerScienceandGeneralIssues ©SpringerInternationalPublishingSwitzerland2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerptsinconnection withreviewsorscholarlyanalysisormaterialsuppliedspecificallyforthepurposeofbeingenteredand executedonacomputersystem,forexclusiveusebythepurchaserofthework.Duplicationofthispublication orpartsthereofispermittedonlyundertheprovisionsoftheCopyrightLawofthePublisher’slocation, inistcurrentversion,andpermissionforusemustalwaysbeobtainedfromSpringer.Permissionsforuse maybeobtainedthroughRightsLinkattheCopyrightClearanceCenter.Violationsareliabletoprosecution undertherespectiveCopyrightLaw. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Whiletheadviceandinformationinthisbookarebelievedtobetrueandaccurateatthedateofpublication, neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityforanyerrorsor omissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,withrespecttothe materialcontainedherein. Typesetting:Camera-readybyauthor,dataconversionbyScientificPublishingServices,Chennai,India Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface This volume contains the papers presented at the 8th International Workshop onReachabilityProblems(RP 2014)heldduring September 22–24,2014,atthe Department of Computer Science, University of Oxford, UK. RP2014wastheeighthintheseriesofworkshops,followingsuccessfulmeet- ingsattheUppsalaUniversity,Sweden,in2013,UniversityofBordeaux,France, in 2012, the University of Genoa, Italy, in 2011, Masaryk University of Brno, CzechRepublic,in2010,EcolePolytechnique,France,in2009,attheUniversity of Liverpool, UK, in 2008, and at Turku University, Finland, in 2007. The aim of the workshop is to bring together scholars from diverse fields with a shared interested in reachability problems. Reachability is a fundamen- tal computational problem that appears in many different contexts: concurrent systems, computational models such as cellular automata and Petri nets, de- cision procedures for logical theories, program analysis, discrete and continu- ous systems, time-critical systems, hybrid systems, rewriting systems, algebraic structures(groups,semigroupsandrings),deterministic ornon-deterministicit- erative maps, probabilistic and parametric systems, and open systems modelled as games. Typically, for a fixed system descriptiongivenin some form (rewriting rules, transformationsbycomputablefunctions,systemsofequations,logicalformulas, etc.) a reachability problem consists in checking whether a given set of target states canbe reachedstartingfroma fixed setof initial states. The setof target states can be represented explicitly or via some implicit representation (e.g., a system of equations, a set of minimal elements with respect to some ordering on the states). Sophisticated quantitative and qualitative properties can often be reduced to basic reachability questions. Decidability and complexity bound- aries, algorithmic solutions, and efficient heuristics are all important aspects to be considered in this context. Algorithmic solutions are often based on differ- ent combinations of exploration strategies, symbolic manipulations of sets of states,decompositionproperties,reductiontooptimisationproblemsandlogical decisionprocedures.Suchalgorithmsalsobenefit fromapproximations,abstrac- tions, accelerations, and extrapolation heuristics. Ad hoc solutions as well as solutions basedon general-purposeconstraintsolversand deduction engines are often combined in order to balance efficiency and flexibility. The purpose of the conference is to promote the exploration of new ap- proaches for the modelling and analysis of computational processes by combin- ingmathematical,algorithmic,andcomputationaltechniques.Topicsofinterest include (but are not limited to): reachability for infinite state systems; rewrit- ing systems; reachability analysis in counter/timed/cellular/communicatingau- tomata; Petri- nets; computational aspects of semigroups, groups, and rings; reachability in dynamical and hybrid systems; frontiers between decidable and VI Preface undecidable reachability problems; complexity and decidability aspects; pre- dictabilityiniterativemapsandnewcomputationalparadigms.Alltheseaspects were discussed in the presentations of the eighth edition of the RP workshop. The proceedings of the previous editions of the workshop appeared in the fol- lowing volumes: MikaHirvensalo,VesaHalava,IgorPotapov,JarkkoKari(Eds.):Proceedingsof the Satellite Workshops of DLT 2007. TUCS General Publication No 45, June 2007. ISBN: 978-952-12-1921-4. Vesa Halava and Igor Potapov (Eds.): Proceedings of the Second Workshop on ReachabilityProblemsinComputationalModels(RP2008).ElectronicNotesin Theoretical Computer Science. Volume 223, Pages 1-264 (26 December 2008). OlivierBournezandIgorPotapov(Eds.):ReachabilityProblems,ThirdInterna- tional Workshop, RP 2009, Palaiseau, France, September 23–25, 2009, Lecture Notes in Computer Science, 5797, Springer 2009. Antonin Kucera and Igor Potapov (Eds.): Reachability Problems, 4th Interna- tional Workshop, RP 2010, Brno, Czech Republic, August 28–29,2010, Lecture Notes in Computer Science, 6227, Springer 2010. GiorgioDelzanno,IgorPotapov(Eds.):ReachabilityProblems,5thInternational Workshop, RP 2011, Genoa, Italy, September 28–30, 2011, Lecture Notes in Computer Science, 6945, Springer 2011. Alain Finkel, Jerome Leroux, Igor Potapov (Eds.): Reachability Problems, 6th International Workshop, RP 2012, Bordeaux, France, September 17-19, 2012. Lecture Notes in Computer Science 7550, Springer 2012. ParoshAziz Abdulla, Igor Potapov (Eds.): Reachability Problems, 7th Interna- tional Workshop, RP 2013, Uppsala, Sweden, September 24-26, 2013. Lecture Notes in Computer Science 8169, Springer 2013. The four keynote speakers at the 2014 conference were: – Byron Cook, UCL and Microsoft Research, UK. – Kousha Etessami, University of Edinburgh, UK. – Anca Muscholl, LaBRI, University of Bordeaux, France. – Sylvain Schmitz, LSV and ENS-Cachan, France. There were 25 submissions. Each submission was reviewed by at least three Program Committee members. The full list of the members of the Program Committeeandthelistofexternalreviewerscanbefoundonthenexttwopages. The ProgramCommittee is grateful for the highly appreciatedand high-quality workproducedbytheseexternalreviewers.Basedonthesereviews,theProgram Preface VII Committee decided to accept 17 papers, in addition to the four invited talks. The workshop also provided the opportunity to researchers to give informal presentations that are prepared very shortly before the event and inform the participants about current researchand work in progress. Wegratefullyacknowledgetheorganizationteamfortheirhelp.Inparticular we wish to thank Andrea Pilot, Renate Henison, Jordan Summers-Young and Elizabeth Walsh. It is alsoa greatpleasure to acknowledgethe team ofthe EasyChairsystem, and the fine cooperation with the Lecture Notes in Computer Science team of Springer, which made the production of this volume possible in time for the conference.Finally,wethankalltheauthorsfortheirhigh-qualitycontributions, and the participants for making this edition of RP 2014 a success. September 2014 Jo¨el Ouaknine Igor Potapov James Worrell Organization Program Committee Marius Bozga Verimag/CNRS, France Thomas Brihaye University of Mons, Belgium V´eronique Bruy`ere University of Mons, Belgium Laurent Doyen LSV, ENS Cachan and CNRS, France John Fearnley University of Liverpool, UK Gilles Geeraerts Universit´e Libre de Bruxelles, Belgium Kim Guldstrand Larsen Aalborg University, Denmark Stefan Go¨ller University of Bremen, Germany Martin Lange University of Kassel, Germany Ranko Lazic University of Warwick, UK Rupak Majumdar MPI-SWS, Germany Nicolas Markey LSV, CNRS and ENS Cachan, France Madhavan Mukund Chennai Mathematical Institute, India Andrzej Murawski University of Warwick, UK Joel Ouaknine Oxford University, UK ParitoshPandya TIFR, India Igor Potapov The University of Liverpool, UK Alexander Rabinovich Tel Aviv University, Israel Tayssir Touili LIAFA, CNRS and University Paris Diderot, France Thomas Wahl Northeastern University, USA James Worrell Oxford University, UK Lijun Zhang DTU, Denmark Additional Reviewers Andr´e, E´tienne Fribourg, Laurent Bertrand, Nathalie Hofman, Piotr Blondin, Michael Praveen, M. Boigelot, Bernard Reichert, Julien Bonnet, Remi Rezine, Ahmed Chistikov, Dmitry Song, Lei Devillers, Raymond Steffen, Martin Donze, Alexandre Turrini, Andrea Forejt, Vojtech Velner, Yaron Abstracts of Invited Talks Algorithms for Branching Markov Decision Processes Kousha Etessami School of Informatics Universityof Edinburgh [email protected] Multi-type branching processes (BPs)are classicstochastic processeswith appli- cationsinmanyareas,includingbiologyandphysics.ABPmodelsthestochastic evolution of a population of entities of distinct types. In each generation, every entity ofeachtype, t, produces a setofentities ofvarioustypes inthe next gen- eration according to a given probability distribution on offsprings for the type t. In a Branching Markov Decision Process (BMDP), there is also a controller whocantakeactionsthataffectthe probabilitydistributionoftheoffspringsfor each entity of each type. For both BPs and BMDPs, the state space consists of all possible populations, given by the number of entities of each type, so there are infinitely many states. Inrecentyearstherehasbeenabodyofresearchaimedatstudyingthecom- putationalcomplexityofkeyanalysisproblemsassociatedwithMDPextensions (and,moregenerallystochastic gameextensions)ofimportantclassesoffinitely- presentedbut (countably) infinite-state stochastic processes, including BMDPs, and closely related models, such as stochastic context-free grammars extended withacontroller.Acentralanalysisproblemforallofthesemodels,whichforms the key to a number of other analyses, is the problem of computing their op- timal termination (extinction) probability. In the setting of BMDPs, these are the maximum (minimum) probabilities, over all control strategies (or policies), starting from a single entity of a given type, that the process will eventually reach extinction (i.e., the state where no entities have survived). From these quantities, one cancompute the optimum probabilityfor anyinitial population, as well as other quantities of interest. OnecanwriteBellmanoptimalityequationsfortheoptimalextinctionprob- abilities of BMDPs, and for a number of related important infinite-state MDP models. These Bellman equations are multivariate systems of monotone proba- bilistic max (or min) polynomial equations, which we call max/minPPSs. They havethe formx =P (x ,...,x ), i=1,...,n,whereeachP (x)≡max q (x) i i 1 n i j i,j (respectivelyP (x)≡min q (x))isthemax(min)overafinitenumberofprob- i j i,j abilistic polynomials, q (x). A probabilistic polynomial, q(x), is a multi-variate i,j polynomial where the monomial coefficients and constant term of q(x) are all non-negative and sum to ≤1. The least fixed point (LFP) solution of such Bell- man equations, corresponding to a given BMDP, captures its vector of optimal extinction probabilities, starting with one object of each type. This talk will surveyalgorithmsfor, and discuss the complexity of, some key analysisproblemsforBMDPs.Inparticular,Iwilldiscussrecentjointworkwith
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