Basic ConceptsWhat is Software Architecture?What is “Principal”?Other Definitions of Software ArchitectureTemporal AspectPrescriptive vs. Descriptive ArchitectureAs-Designed vs. As-Implemented ArchitectureSlide 8Slide 9Architectural EvolutionArchitectural DegradationArchitectural RecoveryImplementation-Level View of an ApplicationSlide 14DeploymentA System’s Deployment Architectural PerspectiveSoftware Architecture’s ElementsComponentsConnectorsExamples of ConnectorsConfigurationsAn Example ConfigurationArchitectural StylesArchitectural PatternsThree-Tiered PatternArchitectural Models, Views, and VisualizationsArchitectural ProcessesStakeholders in a System’s ArchitectureCopyright © Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy. All rights reserved.Basic ConceptsSoftware ArchitectureLecture 32Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureWhat is Software Architecture?Definition:A software system’s architecture is the set of principal design decisions about the systemSoftware architecture is the blueprint for a software system’s construction and evolutionDesign decisions encompass every facet of the system under developmentStructureBehaviorInteractionNon-functional properties3Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureWhat is “Principal”?“Principal” implies a degree of importance that grants a design decision “architectural status”It implies that not all design decisions are architecturalThat is, they do not necessarily impact a system’s architectureHow one defines “principal” will depend on what the stakeholders define as the system goals4Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureOther Definitions of Software ArchitecturePerry and WolfSoftware Architecture = { Elements, Form, Rationale } what how whyShaw and GarlanSoftware architecture [is a level of design that] involves the description of elements from which systems are built, interactions among those elements, patterns that guide their composition, and constraints on these patterns.KruchtenSoftware architecture deals with the design and implementation of the high-level structure of software.Architecture deals with abstraction, decomposition, composition, style, and aesthetics.5Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureTemporal AspectDesign decisions are and unmade over a system’s lifetime Architecture has a temporal aspectAt any given point in time the system has only one architectureA system’s architecture will change over time6Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitecturePrescriptive vs. Descriptive ArchitectureA system’s prescriptive architecture captures the design decisions made prior to the system’s constructionIt is the as-conceived or as-intended architectureA system’s descriptive architecture describes how the system has been builtIt is the as-implemented or as-realized architecture7Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureAs-Designed vs. As-Implemented ArchitectureSoftware Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.8Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureAs-Designed vs. As-Implemented ArchitectureSoftware 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 ArchitectureAs-Designed vs. As-Implemented Architecture Which architecture is “correct”?  Are the two architectures consistent with one another?  What criteria are used to establish the consistency between the two architectures?  On what information is the answer to the preceding questions based? Software 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 ArchitectureArchitectural EvolutionWhen a system evolves, ideally its prescriptive architecture is modified firstIn practice, the system – and thus its descriptive architecture – is often directly modified This happens because ofDeveloper sloppinessPerception of short deadlines which prevent thinking through and documenting Lack of documented prescriptive architectureNeed or desire for code optimizationsInadequate techniques or tool support11Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureArchitectural DegradationTwo related conceptsArchitectural driftArchitectural erosionArchitectural drift is introduction of principal design decisions into a system’s descriptive architecture that are not included in, encompassed by, or implied by the prescriptive architecturebut which do not violate any of the prescriptive architecture’s design decisionsArchitectural erosion is the introduction of architectural design decisions into a system’s descriptive architecture that violate its prescriptive architecture12Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureArchitectural RecoveryIf architectural degradation is allowed to occur, one will be forced to recover the system’s architecture sooner or later Architectural recovery is the process of determining a software system’s architecture from its implementation-level artifactsImplementation-level artifacts can beSource codeExecutable filesJava .class files13Foundations, Theory, and PracticeSoftware ArchitectureSoftware ArchitectureImplementation-Level View of an 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 ArchitectureImplementation-Level View of an ApplicationComplex and virtuallyincomprehensible!Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.15Foundations,