On bounded model checking of asynchronous systems

This dissertation studies the verification of reachability properties of concurrent systems where the components of the system are Labeled Transition Systems (LTSs) using a symbolic model checking technique called Bounded Model Checking (BMC). BMC is a technique that seeks to answer the question whether among the system’s executions shorter than some given number of steps there is one (or more) violating a given property. Answering this question is reduced to propositional satisfiability, i.e., to a propositional formula that is satisfiable iff there is such a violating execution. The translation from a system to a formula is polynomial in the size of the system but the running time of the propositional solver can be exponential in the number of atomic propositions in the formula. This number, on the other hand, correlates directly with the number of execution steps that the formula models. Traditionally, LTSs are model checked by composing the component

Handling Conflicts in Depth-First Search for LTL Tableau to Debug Compliance Based Languages

Providing adequate tools to tackle the problem of inconsistent compliance rules is a critical research topic. This problem is of paramount importance to achieve automatic support for early declarative design and to support evolution of rules in contract-based or service-based systems. In this paper we investigate the problem of extracting temporal unsatisfiable cores in order to detect the inconsistent part of a specification. We extend conflict-driven SAT-solver to provide a new conflict-driven depth-first-search solver for temporal logic. We use this solver to compute LTL unsatisfiable cores without re-exploring the history of the solver.Comment: In Proceedings FLACOS 2011, arXiv:1109.239

tapaustutkimus agenttiteknologioiden soveltamisesta telekommunikaatiopalveluiden tuottamisessa

Agenttisuuntautunut ohjelmointi on ohjelmistoteollisuuden nouseva paradigma. Agentit ovat ohjelmistokomponentteja, jotka kykenevät liikkumaan itsenäisesti tietoverkoissa ja suorittamaan koodiaan verkon eri solmuissa. Laskenta suoritetaan näin paikallisesti vähentäen verkon kuormitusta verkon yli tapahtuvaan kommunikaatioon verrattuna. Edistysaskeleet telekommunikaatiossa ovat johtaneet tilanteeseen, jossa verkon operaattorit voivat tarjota moninaisia, tavallista puhelua monimutkaisempia palveluja, joilla on kaupallista arvoa. Lisäksi markkinoiden vapautuminen on johtanut tilanteeseen, jossa samankaltaista palvelua tarjoaa useita keskenään kilpailevaa yrittäjää. Tämä työ esittelee tapaustutkimuksen siitä, miten agenttiteknologioita voidaan soveltaa parhaan tarjouksen löytämiseksi kilpailluilla markkinoilla käyttäjän tarvitsematta puuttua asiaan. Halutulla palvelulla on multimediasisältö ja tarjousten vertailu tehdään perustuen median tekniseen laatuun ja palvelun hintaan. Työ käsittelee myös henkilökohtaisen liikkuvuuden tukemista, palvelun etsintä on mahdollista käyttäjän sijainnista riippumatta. Avoimessa kaupallisia palveluita tarjoavassa ympäristössä käyttäjien autentikointi on luonnollisesti tärkeää. Työn keskeinen sisältö on ehdotus käyttäjien autentikointiin ja tietojen hallintaan liittyvästä ohjelmistototeutuksesta. Henkilökohtainen liikkuvuus on toteutettu siten, että käyttäjä voi kirjoittautua sisään järjestelmään missä tahansa ja tiedot kulkevat liikkuvan agentin mukana. Ohjelmisto on kirjoitettu VTT Tietotekniikan palveluksessa ja se on osa ACTS-projekti MONTAGEa

BOUNDED MODEL CHECKING FOR VERIFYING CONCURRENT PROGRAMS

Teknillisen korkeakoulun tietojenkäsittelyteorian laboratorion tutkimusraportti 7

Software Tools for Technology Transfer manuscript No. (will be inserted by the editor) BMC via On-the-Fly Determinization

The date of receipt and acceptance will be inserted by the editor Abstract. This paper develops novel bounded model checking (BMC) techniques for asynchronous parallel systems. The aim is to increase the efficiency of BMC by exploiting the inherent concurrency in such systems. This added efficiency is gained by covering more reachable states within a given bound using two techniques. Firstly, a non-standard execution model, step executions, where multiple actions can take place simultaneously is applied. Secondly, the number of executions the system can have is reduced by modeling the execution of the system components as if they were determinized. This determinization technique also enables the removal of the internal transitions of the components. Step executions can be further restricted to a subclass called process executions without losing any reachable states. The paper presents a translation scheme for bounded model checking of reachability properties. The translation is from an asynchronous system where the components are modeled as labeled transition systems (LTSs) to a propositional formula. The models of the formula correspond to the step executions of the original system where each component is replaced with its determinized counterpart. The formula for step executions can be easily extended in such a way that its models correspond to the process executions of the system. The translation scheme has been implemented and some experimental comparisons performed. The results show that the bound needed to detect a violation of a reachability property is for step and process executions in most cases lower than in interleavin