PATTERN-ORIENTED S O F T W A R E ARCHITECTURE P A T T E R N - O R I E N T E D S O F T W A R E A R C H I T E C T U R E A Pattern Language for Distributed Computing Volume 4 Frank Buschmann, Siemens, Munich,Germany Kevlin Henney, Curbralan,Bristol,UK DouglasC. Schmidt, VanderbiltUniversity, Tennessee,USA Copyright2007 JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester, WestSussexPO198SQ,England Telephone(+44)1243779777 Email(forordersandcustomerserviceenquiries):[email protected] VisitourHomePageonwww.wileyeurope.comorwww.wiley.com AllRightsReserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystemor transmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recording, scanningorotherwise,exceptunderthetermsoftheCopyright,DesignsandPatentsAct1988or underthetermsofalicenceissuedbytheCopyrightLicensingAgencyLtd,90TottenhamCourt Road,LondonW1T4LP,UK,withoutthepermissioninwritingofthePublisher.Requeststothe PublishershouldbeaddressedtothePermissionsDepartment,JohnWiley&SonsLtd,The Atrium,SouthernGate,Chichester,WestSussexPO198SQ,England,oremailedto [email protected],orfaxedto(+44)1243770620. FrontcoverImageCopyright2007YannArthus-Bertrand/Altitude Designationsusedbycompaniestodistinguishtheirproductsareoftenclaimedastrademarks. Allbrandnamesandproductnamesusedinthisbookaretradenames,servicemarks, trademarksorregisteredtrademarksoftheirrespectiveowners.ThePublisherisnotassociated withanyproductorvendormentionedinthisbook. Thispublicationisdesignedtoprovideaccurateandauthoritativeinformationinregardtothe subjectmattercovered.ItissoldontheunderstandingthatthePublisherisnotengagedin renderingprofessionalservices.Ifprofessionaladviceorotherexpertassistanceisrequired,the servicesofacompetentprofessionalshouldbesought. OtherWileyEditorialOffices JohnWiley&SonsInc.,111RiverStreet,Hoboken,NJ07030,USA Jossey-Bass,989MarketStreet,SanFrancisco,CA94103-1741,USA Wiley-VCHVerlagGmbH,Boschstr.12,D-69469Weinheim,Germany JohnWiley&SonsAustraliaLtd,42McDougallStreet,Milton,Queensland4064,Australia JohnWiley&Sons(Asia)PteLtd,2ClementiLoop#02-01,JinXingDistripark,Singapore129809 JohnWiley&SonsCanadaLtd,6045FreemontBlvd,Mississauga,Ontario,L5R4J3,Canada Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappears inprintmaynotbeavailableinelectronicbooks. BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN-13:978-0-470-05902-9(hbk) Typesetin10/13Bookman-LightbyLaserwordsPrivateLimited,Chennai,India PrintedandboundinGreatBritainbyBell&Bain,Glasgow Thisbookisprintedonacid-freepaperresponsiblymanufacturedfromsustainableforestry inwhichatleasttwotreesareplantedforeachoneusedforpaperproduction. For Anna, Bebe´†, and Martina Frank Buschmann For Carolyn, Stefan, and Yannick Kevlin Henney For Lori, Bronson, Mom, and Dad DouglasC.Schmidt † Bebe´,July3,1999 Table of Contents Foreword . . . . . . . . . . . . . . . . . . . . . xv About This Book . . . . . . . . . . . . . . . . . xvii About The Authors . . . . . . . . . . . . . . . xxiii Guide To The Reader . . . . . . . . . . . . . . xxvii Part I Some Concepts . . . . . . . . . . . . . . . . . . 1 1 On Patterns and Pattern Languages . . . . . 3 1.1 Patterns Introduced . . . . . . . . . . . . . . . . . 4 1.2 Inside Patterns . . . . . . . . . . . . . . . . . . . . 6 1.3 Between Patterns . . . . . . . . . . . . . . . . . . 10 1.4 Into Pattern Languages . . . . . . . . . . . . . . . 13 1.5 Patterns Connected . . . . . . . . . . . . . . . . . 15 2 On Distributed Systems . . . . . . . . . . . . 17 2.1 Benefits of Distribution . . . . . . . . . . . . . . 18 2.2 Challenges of Distribution . . . . . . . . . . . . . 20 2.3 Technologies for Supporting Distribution . . . 22 2.4 Limitations of Middleware . . . . . . . . . . . . . 32 3 On the Pattern Language . . . . . . . . . . . . 33 3.1 Intent, Scope, and Audience . . . . . . . . . . . 34 3.2 Origins and Genesis . . . . . . . . . . . . . . . . 35