Anton Tarasyuk Formal Development and Quantitative Verification of Dependable Systems PDF
Preview Anton Tarasyuk Formal Development and Quantitative Verification of Dependable Systems
Anton Tarasyuk Formal Development and Quantitative Verification of Dependable Systems Turku Centre for Computer Science TUCS Dissertations No 156, January 2013 Formal Development and Quantitative Verification of Dependable Systems Anton Tarasyuk To be presented, with the permission of the Department of Information Technologies of the ˚Abo Akademi University, for public criticism in Auditorium Gamma on January 28, 2013, at 12 noon. Turku Centre for Computer Science ˚Abo Akademi University Department of Information Technologies Joukahaisenkatu 3-5, 20520 Turku Finland 2013 Supervisors Docent Elena Troubitsyna Department of Information Technologies ˚Abo Akademi University Joukahaisenkatu 3-5 A, 20520 Turku Finland Docent Linas Laibinis Department of Information Technologies ˚Abo Akademi University Joukahaisenkatu 3-5 A, 20520 Turku Finland Reviewers Professor Dominique M´ery LORIA & Universit´e de Lorraine F-54506 Vandoeuvre l`es Nancy France Professor Aad van Moorsel School of Computing Science Newcastle University Newcastle upon Tyne, NE1 7RU United Kingdom Opponent Professor Aad van Moorsel School of Computing Science Newcastle University Newcastle upon Tyne, NE1 7RU United Kingdom ISBN 978-952-12-2832-2 ISSN 1239-1883 To my mother Ìîåé ìàìå ïîñâÿùàåòñÿ i It is good to have an end to journey towards; but it is the journey that matters, in the end. Ursula K. Le Guin, “The Left Hand of Darkness” ii Abstract Modern software-intensive systems are becoming increasingly complex. Yet weareobservingthepervasiveuseofsoftwareinsuchcriticalinfrastructures as transportation systems, healthcare, telecommunication, energy produc- tion, etc. Consequently, we tend to place increasing reliance on computer- basedsystemsandthesoftwarethattheyarerunning. Thedegreeofreliance that we can justifiably place on a system is expressed by the notion of de- pendability. Designing highly-dependable systems is a notoriously difficult task. It requires rigorous mathematical methods to prevent design errors and guar- antee the correct and predictable system behaviour. However, fault pre- vention via rigorous engineering still cannot ensure avoidance of all faults. Hence we need powerful mechanisms for tolerating faults, i.e., the solutions that allow the system to confine the damage caused by fault occurrence and guarantee high reliability and safety. Traditionally, such dependabil- ity attributes are assessed probabilistically. However, the current software development methods suffer from discontinuity between modelling the func- tional system behaviour and probabilistic dependability evaluation. To ad- dress these issues, in the thesis we aim at establishing foundations for a rigorous dependability-explicit development process. In particular, we pro- pose a semantic extension of Event-B – an automated state-based formal development framework – with a possibility of quantitative (probabilistic) reasoning. Event-Banditsassociateddevelopmenttechnique–refinement– providethedesignerswithapowerfulframeworkforcorrect-by-construction systems development. Via abstract modelling, proofs and decomposition it allows the designers to derive robust system architectures, ensure pre- dictable system behaviour and guarantee preservation of important system properties. We argue that the rigorous refinement-based approach to system devel- opment augmented with probabilistic analysis of dependability significantly facilitates development of complex software systems. Indeed, the proposed probabilistic extension of Event-B allows the designers to quantitatively as- sesstheeffectofdifferentfaulttolerancemechanismsandarchitecturalsolu- tionsonsystemdependability. Moreover, itenablesthestochasticreasoning iii about the impact of component failures and repairs on system reliability and safety from the early design stages. The proposed enhanced version of the standard Event-B refinement allows the designers to ensure that the developed system is not only correct-by-construction but also dependable- by-construction, i.e., it guarantees that refinement improves (or at least preserves) the probabilistic measure of system dependability. The proposed extension has been validated by a number of case stud- ies from a variety of application domains, including service-oriented sys- tems, aerospace, railways and communicating systems. We believe that the research presented in the thesis contributes to creating an integrated dependability-explicit engineering approach that facilitates rigorous devel- opment of complex computer-based systems. iv Sammanfattning Programvaruintensiva system ¨okar allt mera i komplexitet, men trots detta anv¨andsprogramvaraikritiskinfrastrukturinomomr˚adens˚asomtransport, telekommunikation, h¨alsov˚ard och energiproduktion. Vi litar allt mera p˚a datorbaserade system och deras programvara, och graden till vilken vi kan lita p˚a ett system beskriver vi med uttrycket p˚alitlighet. Att utveckla starkt p˚alitliga system ¨ar erk¨ant sv˚art, och kr¨aver rigor¨osa matematiska metoder f¨or att f¨orhindra designfel och garantera att syste- met uppf¨or sig korrekt och f¨orutsebart. Dessa metoder kan dock inte ga- rantera att alla fel undviks, och d¨arf¨or beh¨ovs kraftfulla mekanismer f¨or feltolerans, dvs. l¨osningar som g¨or det m¨ojligt f¨or systemet att f¨orhindra spridningen av den skada som felet orsakade samt garantera h¨og p˚alitlighet och s¨akerhet. Dessa egenskaper utv¨arderas traditionellt probabilistiskt, men i de utvecklingsmetoder som anv¨ands i dag finns det ingen kontinuitet mel- lanmodelleringavsystemetsfunktionalitetochprobabilistiskutv¨arderingav p˚alitligheten.Idennaavhandling¨arv˚arm˚als¨attningattetableragrunderf¨or en rigor¨os utvecklingsmetod med explicit p˚alitlighet. Specifikt f¨oresl˚ar vi ett semantiskttill¨aggtillEvent-B–ettautomeratramverkf¨ortillst˚andsbaserad formell utveckling – som till˚ater ett kvantitativt (probabilistiskt) resone- mang. Event-B och dess tillh¨orande utvecklingsteknik – precisering – ger ett kraftfullt ramverk f¨or utveckling av system som ¨ar korrekta genom kon- struktionen. Detta g¨or det m¨ojligt att via abstrakt modellering, bevis och dekomposition skapa robusta systemarkitekturer och f¨ors¨akra sig om att sy- stemets uppf¨orande ¨ar f¨orutsebart och att viktiga egenskaper hos systemet bevaras under systemets exekvering. Vi h¨avdar att utvecklingen av p˚alitliga komplexa system underl¨attas av rigor¨ospreciseringsbaseradsystemutvecklingkombineradmedprobabilistisk analysavp˚alitlighet.Detf¨oreslagnaprobabilistiskatill¨aggettillEvent-Bg¨or det m¨ojligt att kvantitativt uppskatta effekten av olika feltoleransmekanis- mer och arkitekturbaserade l¨osningar p˚a systemens p˚alitlighet. Dessutom m¨ojligg¨or det redan fr˚an ett tidigt stadium stokastiskt resonemang om vil- ken effekt komponentfel och -reparationer har p˚a systemets p˚alitlighet och s¨akerhet. Den f¨oreslagna f¨orb¨attrade versionen av preciseringen i Event-B g¨or det m¨ojligt att s¨akerst¨alla att systemet som utvecklas inte enbart ¨ar v korrekt genom konstruktionen, utan ocks˚a p˚alitligt genom konstruktionen, dvs. garanterar att preciseringen f¨orb¨attrar, eller˚atminstone bibeh˚aller det sannolikhetsbaserade m˚attet av systemets p˚alitlighet. Det f¨oreslagna till¨agget har validerats av ett antal fallstudier inom olika applikationsomr˚aden, vilka inkluderar serviceinriktade system, flygindustri, sp˚artrafik och kommunikationssystem. Vi tror att forskningen som presen- teras i denna avhandling medverkar till att skapa en integrerad utvecklings- teknik som har explicit p˚alitlighet och underl¨attar rigor¨os utveckling av komplexa datorbaserade system. vi
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