A Process Algebraic Approach to Software Architecture Design

315 Pages·2010·3.575 MB·English

by  Alessandro Aldini, Marco Bernardo, Flavio Corradini (auth.)

A Process Algebraic Approach to Software
Architecture Design

Alessandro Aldini (cid:129) Marco Bernardo
Flavio Corradini
A Process Algebraic
Approach to Software
Architecture Design
123
AlessandroAldini FlavioCorradini
Universita`diUrbino Universita`diCamerino
Ist.diScienzeeTecnologiedell’Informazione Dip.todiMatematicaeInformatica
PiazzadellaRepubblica13 ViaMadonnadelleCarceri9
61029Urbino 62032Camerino
Italy Italy
[email protected] fl[email protected]
MarcoBernardo
Universita`diUrbino
Ist.diScienzeeTecnologiedell’Informazione
PiazzadellaRepubblica13
61029Urbino
Italy
[email protected]
ISBN978-1-84800-222-7 e-ISBN978-1-84800-223-4
DOI10.1007/978-1-84800-223-4
SpringerLondonDordrechtHeidelbergNewYork
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Preface
Inthefieldofformalmethodsincomputerscience,concurrencytheoryisreceivinga
constantlyincreasinginterest.Thisisespeciallytrueforprocessalgebra.Althoughit
hadbeenoriginallyconceivedasameansforreasoningaboutthesemanticsofcon-
current programs, process algebraic formalisms like CCS, CSP, ACP, π-calculus,
andtheirextensions(see,e.g.,[154,119,112,22,155,181,30])weresoonusedalso
forcomprehendingfunctionalandnonfunctionalaspectsofthebehaviorofcommu-
nicatingconcurrentsystems.
Thescientificimpactofprocesscalculiandbehavioralequivalencesatthebase
ofprocessalgebraiswitnessednotonlybyaveryrichliterature.Itisinfactworth
mentioningthestandardizationprocedurethatledtothedevelopmentoftheprocess
algebraiclanguageLOTOS[49],aswellastheimplementationofseveralmodeling
andanalysistoolsbasedonprocessalgebra,likeCWB[70]andCADP[93],some
of which have been used in industrial case studies. Furthermore, process calculi
andbehavioralequivalencesarebynowadoptedinuniversity-levelcoursestoteach
the foundationsofconcurrentprogrammingaswell as the model-drivendesign of
concurrent,distributed,andmobilesystems.
Nevertheless, after 30 years since its introduction, process algebra is rarely
adopted in the practice of software development.On the one hand, its technicali-
ties often obfuscate the way in which systems are modeled. As an example, if a
processtermcomprisesnumerousoccurrencesoftheparallelcompositionoperator,
itishardtounderstandthecommunicationschemeamongthevarioussubterms.On
the other hand, process algebra is perceived as being difficult to learn and use by
practitioners, as it is not close enough to the way they think of software systems.
Forinstance,processalgebrainherentlysupportscompositionalityandabstraction,
butitdoesnotsupportwidespreadparadigmslikeobjectorientationandcomponent
orientation.Asaconsequence,processalgebracannotcompetewithcommonlyac-
ceptednotationslikeUML,althoughitismorerobustthanthem.
Some years ago, we thus began to address the following problem:How to en-
hancetheusabilityofprocessalgebra?
We think thatan answer to this questionshould take the followingthreeissues
intoaccount.Firstly,itisnecessarytosupportafriendlycomponent-orientedwayof
vii
viii Preface
modelingsystemswithprocessalgebra,sothatthesoftwaredesignercanreasonin
termsofcomposablesoftwareunitswithouthavingtoworryaboutprocessalgebra
technicalities.Secondly,itisnecessarytoprovideanefficientcomponent-oriented
wayofanalyzingfunctionalandnonfunctionalpropertiesofsystemsmodeledwith
process algebra, and to return component-oriented diagnostic information in the
casethatpropertyviolationsaredetected.Thirdly,itisnecessarytointegrateprocess
algebrainthesoftwaredevelopmentprocess,whichamountstosingleoutthephases
inwhichitcanbeusefullyemployed.
Startingfromthelastissue, we believethata goodchoiceis thatofworkingat
thesoftwarearchitecturelevelofdesign.Infact,asoftwarearchitectureelucidates
the elementsconstitutinga system, their interactions,and the constraintson those
elements and their interactions that provide a framework in which to satisfy the
requirementsandserveasabasisforthesubsequentdevelopmentphases[169,184].
Sincethefocusisnotonalgorithmsanddatastructures,butonsoftwarecomponents
andconnectors,asimplicitlydemonstratedin[18]thisistherightabstractionlevel
foraformaldescriptiontechniquelikeprocessalgebra.
We also believe that using process algebra in the architectural design phase is
beneficial for the development process. The architecture of a software system is
typicallyrepresentedasadocumentexpressedinsomegraphicalmodelingnotation
orarchitecturaldescriptionlanguage.Thisdocument,whichshowssystemstructure
andbehavioratahighlevelofabstraction,shouldbesharedbyallthepeoplewho
contributetothevariousphasesofthesoftwaredevelopmentprocess.Thankstoits
precisesemanticsanditsverificationtechniques,processalgebracanplayarolein
theformalizationofthisdocument.Inparticular,itopensthewaytothepossibility
ofanalyzingbehavioralpropertiesintheearlystagesofsoftwaredevelopment[45],
whichhasthe advantageof avoidingdelaysandcoststhatmaybeincurreddueto
thelatediscoveryoferrors.
Inviewofsuchanarchitecturalupgradeofprocessalgebra,ouroriginalquestion
can be refinedasfollows: Howto transformprocess algebraintoan architectural
descriptionlanguage?Howto drive the whole software developmentprocess with
theresultingprocessalgebraicarchitecturaldescriptionlanguage?
The second part of the book is devoted to answering these two questions.
This is accomplishedby constructinga processalgebraic architecturaldescription
language and endowing it with a number of methods dealing with component-
oriented functional verification, component-oriented performance evaluation, and
thearchitecture-levelintegrationofdependabilityandperformance.
The second part comprises of four chapters. In Chap. 4, we provide a number
of guidelinesfor transformingprocessalgebrainto a full-fledgedarchitecturalde-
scription language called PADL. In Chap. 5, we illustrate MISMDET, a topologi-
calreductionprocessforthedetectionofarchitecture-levelmismatches,whichre-
lies on behavioral equivalences and exploits their congruence properties for effi-
ciency reasons and their modallogic characterizationsfor diagnostic purposes. In
Chap. 6, we present PERFSEL, a procedure for the performance-driven selection
among alternative architectural designs, which is based on equipping process al-
gebraic architectural descriptions with queueing network models allowing for the
Preface ix
assessmentofsystem-levelandcomponent-levelperformancemeasures.Finally,in
Chap.7wediscussDEPPERF,amethodologyfortradingdependabilityfeaturesand
performanceindicesinthearchitecturaldesignphase,whichbuildsonequivalence-
checking-basednoninterferenceanalysisandstandardnumericaltechniques.
The first part of the book instead provides backgroundmaterial on syntax and
semantics for process calculi as well as on the bisimulation approach [168,113],
the testing approach[82,111], and the trace approach[57] to the definitionof be-
havioralequivalences.Thisisusefulforadeeperunderstandingofthesecondpart,
asitreportsonmanyconceptsandresultsofprocessalgebratheoryinaquickand
comparativeway.
Thefirstpartcomprisesofthreechapters.InChap.1,weintroduceaprocesscal-
culusinwhichnonotionoftime,probability,orpriorityisassociatedwithactions.
Inordertorepresentreal-timesystems,inChap.2wediscusstwodeterministically
timed extensions of the original process calculus. The first one allows for delays
betweenthe executionofconsecutiveactions,whereasthesecondoneassignsdu-
rationsto actions,with bothdelaysanddurationsbeingexpressedthroughnatural
numbers.In orderto representshared-resourcesystems, in Chap. 3 we illustrate a
stochasticallytimedextensionoftheoriginalprocesscalculus,inwhichactionsare
durational.Sincedurationsarequantifiedthroughexponentiallydistributedrandom
variables,thestochasticprocessgoverningthesystemevolutionovertimeturnsout
tobeacontinuous-timeMarkovchain.
InChaps.1and3,wealsoshowcongruenceproperties,soundandcompleteax-
iomatizations,modallogiccharacterizations,andverificationalgorithmsfornonde-
terministicandMarkovianversionsofbisimulation,testing,andtraceequivalences.
Moreover,following and extending[98], both in the nondeterministiccase and in
theMarkoviancasewecomparethediscriminatingpoweroftheconsideredbehav-
ioralequivalencesandsomeoftheirvariants.Incontrast,inChap.2weconcentrate
onlyonthepropertiesofthebisimulationapproach.Then,weexaminedifferentop-
tions related to the representation of time and time passing – durationless actions
versusdurationalactions,relativetimeversusabsolutetime,globalclockversuslo-
cal clocks– as well as eager,lazy,and maximalprogressinterpretationsof action
execution,inordertostudytheirexpressiveness.
Thisbookisintendedforgraduatestudentsandsoftwareprofessionals.Itcovers
differenttopicssuchasconcurrencytheory,softwarearchitecture,systemmodeling
and verification,and dependabilityand performanceevaluation.These topicsmay
seemunrelated,butinrealitytheyaredeeplyintertwinedandshouldallbepartof
an integrated view in order to manage successfully the increasing complexity of
recentsoftwaresystems.Althoughitcanbeusedinacourseonformalmethodsin
computerscience,thebookdoesnotfocusonlyontheoreticalaspects.Infact,italso
addresses methodological issues and contains application examples. Moreover, it
givesthesameimportancetofunctionalandnonfunctionalaspectsofsystems,inan
attemptto overcomethe drawbacksarisingfromtheirseparateconsideration[88].
The book can thus be used also in a course on model-driven design of software
architectures,inwhichcaseonlyitssecondpartmaybepresented,withconceptsof
itsfirstpartbeingrecalledwhenevernecessary.
x Preface
WewishtothankourcolleaguesattheUniversitiesofUrbinoandCamerino,as
wellasourformercolleaguesattheUniversitiesofBologna,L’Aquila,andTorino,
formanyfruitfuldiscussionsovertheyears.
We are gratefulto all the peoplewith whomwe have collaboratedin the fields
of process algebra and software architecture, in particular: Simonetta Balsamo,
Antonia Bertolino, Edoardo Bonta`, Mario Bravetti, Nadia Busi, Diletta Romana
Cacciagrano, Paolo Ciancarini, Rance Cleaveland, Rocco De Nicola, Maria Rita
DiBerardini,AlessandraDiPierro,LorenzoDonatiello,FrancescoFranze`,Roberto
Gorrieri,PaolaInverardi,JeffKramer,JeffMagee,HenryMuccini,MarcoPistore,
Marina Ribaudo, Marco Roccetti, Marta Simeoni, Angelo Troina, Walter Vogler,
andAlexWolf.
ManythanksalsotoErikdeVink,DiegoLatella,MicheleLoreti,MiekeMassink,
Henry Muccini, and Jeremy Sproston for their kind willingness to review early
drafts of the book, and to Vittorio Cortellessa for having given on several occa-
sionstheopportunitytothesecondauthorofpresentingthesecondpartofthebook
asalectureseriesattheUniversityofL’Aquila.
Finally,wewouldliketothankourfamiliesfortheirpatienceandtolerancedur-
ingthewritingofthisbook.
Urbino,Italy AlessandroAldini
Urbino,Italy MarcoBernardo
Camerino,Italy FlavioCorradini