Architectural StylesObject-Oriented StyleObject-Oriented LLOO/LL in UMLLayered StyleLayered Style (cont’d)Slide 7Layered Systems/Virtual MachinesLayered LLClient-Server StyleClient-Server LLData-Flow StylesBatch-Sequential: A Financial ApplicationBatch-Sequential LLPipe and Filter StylePipe and Filter (cont’d)Slide 17Pipe and Filter LLBlackboard StyleBlackboard LLRule-Based StyleRule-Based Style (cont’d)Rule Based LLInterpreter StyleInterpreter LLMobile-Code StyleMobile Code LLImplicit Invocation StyleImplicit Invocation (cont’d)Publish-SubscribePublish-Subscribe (cont’d)Pub-Sub LLEvent-Based StyleEvent-based LLPeer-to-Peer StylePeer-to-Peer Style (cont’d)Peer-to-Peer LLCopyright © Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy. All rights reserved.Architectural StylesSoftware ArchitectureLecture 52Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureObject-Oriented StyleComponents are objectsData and associated operationsConnectors are messages and method invocationsStyle invariantsObjects are responsible for their internal representation integrityInternal representation is hidden from other objectsAdvantages“Infinite malleability” of object internalsSystem decomposition into sets of interacting agentsDisadvantagesObjects must know identities of serversSide effects in object method invocations3Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureObject-Oriented LLSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.4Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureOO/LL in UMLSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.5Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureLayered StyleHierarchical system organization“Multi-level client-server”Each layer exposes an interface (API) to be used by above layersEach layer acts as aServer: service provider to layers “above”Client: service consumer of layer(s) “below”Connectors are protocols of layer interactionExample: operating systemsVirtual machine style results from fully opaque layers6Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureLayered Style (cont’d)AdvantagesIncreasing abstraction levelsEvolvabilityChanges in a layer affect at most the adjacent two layersReuseDifferent implementations of layer are allowed as long as interface is preservedStandardized layer interfaces for libraries and frameworks7Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureLayered Style (cont’d)DisadvantagesNot universally applicablePerformanceLayers may have to be skippedDetermining the correct abstraction level8Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureLayered Systems/Virtual MachinesSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.9Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureLayered LLSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.10Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureClient-Server StyleComponents are clients and serversServers do not know number or identities of clientsClients know server’s identityConnectors are RPC-based network interaction protocols11Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureClient-Server LLSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.12Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureData-Flow StylesBatch SequentialSeparate programs are executed in order; data is passed as an aggregate from one program to the next.Connectors: “The human hand” carrying tapes between the programs, a.k.a. “sneaker-net ”Data Elements: Explicit, aggregate elements passed from one component to the next upon completion of the producing program’s execution.Typical uses: Transaction processing in financial systems. “The Granddaddy of Styles”13Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureBatch-Sequential: A Financial ApplicationSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.14Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureBatch-Sequential LLNot a recipe for a successful lunar mission!Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.15Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitecturePipe and Filter StyleComponents are filtersTransform input data streams into output data streamsPossibly incremental production of outputConnectors are pipesConduits for data streamsStyle invariantsFilters are independent (no shared state) Filter has no knowledge of up- or down-stream filtersExamplesUNIX shell signal processingDistributed systems parallel programmingExample: ls invoices | grep -e August | sort16Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitecturePipe and Filter (cont’d)VariationsPipelines — linear sequences of filtersBounded pipes — limited amount of data on a pipeTyped pipes — data strongly typedAdvantagesSystem behavior is a succession of component behaviorsFilter addition, replacement, and reusePossible to hook any two filters together Certain analysesThroughput, latency, deadlockConcurrent execution17Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitecturePipe and Filter (cont’d)DisadvantagesBatch organization of processingInteractive applicationsLowest common denominator on data