Software Architecture
اسلاید 1: Software ArchitectureCIS 376Bruce R. MaximUM-Dearborn
اسلاید 2: Software ArchitectureArchitectural Designprocess for identifying the subsystems that make up a systemdefines framework for sub-system control and communicationSoftware Architecturedescription of the system output by architectural design
اسلاید 3: Architectural Design ProcessSystem structuringsystem decomposed into several subsystemssubsystem communication is establishedControl modelingmodel of control relationships among system components is establishedModular decompositionidentified subsystems decomposed into modules
اسلاید 4: Architectural ModelsStatic structural modelshows major system componentsDynamic process modelshows process structure of the systemInterface modeldefines subsystem interfacesRelationships modeldata flow or control flow diagrams
اسلاید 5: Sommerville discusses several architectural models
اسلاید 6: CASE Repository Model
اسلاید 7: Call-Return Model
اسلاید 8: Real-Time System Control Model
اسلاید 9: Selective Broadcasting Model
اسلاید 10: Interrupt-Driven Control Model
اسلاید 11: Compiler Model
اسلاید 12: OSI Reference ModelApplication
اسلاید 13: Distributed SystemsMost large computer systems are implemented as distributed systemsInformation is also distributed over several computers rather than being confined to a single machineDistributed software engineering has become very important
اسلاید 14: System TypesPersonal systemsdesigned to run on a single user systemEmbedded systemsmay run on a single processormight run on an integrated group of processorsDistributed systemssystem software runs on loosely integrated group of cooperating processors linked by a network
اسلاید 15: Distributed SystemsCharacteristicsResource sharingOpennessConcurrencyScalableFault tolerantTransparentConcernsComplexityCommunicationSecurityManageabilityQuality of ServiceUnpredictability
اسلاید 16: Distributed Systems ArchitecturesClient/Serveroffer distributed services which may be called by clientsservers providing services are treated differently than clients using the servicesDistributed Objectno distinctions made between clients and serversany system object may provide and use services from any other system object
اسلاید 17: MiddlewareSoftware that manages and supports the different components of a distributes systemSits in the middle of the system to broker service requests among componentsUsually off-the-shelf products rather than customRepresentative architecturesCORBA (ORB)COM (Microsoft)JavaBeans (Sun)
اسلاید 18: Multiprocessor ArchitectureSimplest distributed system modelSystem composed of multiple processes that may execute on different processorsModel used in many large real-time systemsDistribution of processes to processors may be preordered or may be under control of a dispatcher
اسلاید 19: Multiprocessor Traffic Control System from Sommerville
اسلاید 20: Client/Server ArchitecturesApplication is modeled as a set of services that are provided by servers and a set of clients that use these servicesClients know the servers but the servers do not need to know all the clientsClients and servers are logical processes (not always physical machines)The mapping of processes to processors is not always 1:1
اسلاید 21: Client/Server System from Sommerville
اسلاید 22: Representative Client/Server Systems Part 1File serversclient requests selected records from a fileserver transmits records to client over the networkDatabase serversclient sends SQL requests to serverserver processes the requestserver returns the results to the client over the network
اسلاید 23: Representative Client/Server Systems part 2Transaction serversclient sends requests that invokes remote procedures on the server sideserver executes procedures invoked and returns the results to the clientGroupware serversserver provides set of applications that enable communication among clients using text, images, bulletin boards, video, etc.
اسلاید 24: Client/Server Software ComponentsUser interaction/presentation subsystemApplication subsystemimplements requirements defined by the application within the context of the operating environment components may reside on either client or server sideDatabase management subsystemMiddlewareall software components that exist on both the client and the server to allow exchange of information
اسلاید 25: Representative Client/Server Configurations - part 1Distributed presentationdatabase and application logic remain on the serverclient software reformats server data into GUI formatRemote presentationsimilar to distributed presentationprimary database and application logic remain on the serverdata sent by the server is used by the client to prepare the user presentation
اسلاید 26: Representative Client/Server Configurations - part 2Distributed logicclient is assigned all user presentation tasks associated with data entry and formulating server queriesserver is assigned data management tasks and updates information based on user actions Remote data managementapplications on server side create new data sourcesapplications on client side process the new data returned by the server
اسلاید 27: Representative Client/Server Configurations - part 3Distributed databasesdata is spread across multiple clients and serversrequires clients to support data management as well as application and GUI componentsFat servermost software functions for C/S system are allocated to the server Thin clientsnetwork computer approach relegating all application processing to a fat server
اسلاید 28: Thin Client ModelUsed when legacy systems are migrated to client server architecturesthe legacy system may act as a server in its own rightthe GUI may be implemented on a clientIt chief disadvantage is that it places a heavy processing load on both the server and the network
اسلاید 29: Fat Client ModelMore processing is delegated to the client as the application processing is locally extendedSuitable for new client/server systems when the client system capabilities are known in advanceMore complex than thin client model with respect to management issuesNew versions of each application need to installed on every client
اسلاید 30: Three-tier ArchitectureEach application architecture layers (presentation, application, database) may run on separate processorsAllows for better performance than a thin-client approachSimpler to manage than fat client approachHighly scalable (as demands increase add more servers)
اسلاید 31: Three-Tier Architecture from Sommerville
اسلاید 32: Guidelines for Distributing Application SubsystemsThe presentation/interaction subsystem is generally placed on the client.If the database is to be shared by multiple users connected by a LAN, the database is typically located on the server.Static data used for reference should be allocated to the client.
اسلاید 33: Linking Client/Server Software SubsystemsPipespermit messaging between different machines running different operating systemsRemote procedure callspermit process running on one machine to invoke execute of process residing on another machineClient/server SQL interactionSQL requests passed from client to server DBMS, this mechanism is limited to RDBMS
اسلاید 34: Design Issues for Client/Server Systems - part 1Data and architectural designdominates the design process to be able to effectively use the capabilities of RDBMS or OODMBSEvent-driven paradigmwhen used, behavioral modeling should be conductedthe control-oriented aspects of the behavioral model should translated into the design model
اسلاید 35: Design Issues for Client/Server Systems - part 2Interface designelevated in importanceuser interaction/presentation component implements all functions associated with a GUIObject-oriented point of viewoften chosen, since object structure is provided by events initiated in the GUI and their event handlers within the client-based software
اسلاید 36: Architectural Design for Client/Server Systems - part 1Best described as communicating processes style architectureArchitectural goal is to achieve easy scalability when adding and arbitrary number of clientsModern C/S systems tend to be component-basedAn object request broker (ORB) architecture is used for implementation
اسلاید 37: Architectural Design for Client/Server Systems - part 2Object adapters or wrappers facilitate communication among clients and serverscomponent implementations are registeredall component references are interpreted and reconciledcomponent references are mapped to corresponding component implementationsobjects are activated and deactivatedoperations are invoked when messages are transmittedsecurity features are implemented
اسلاید 38: Client/Server Design Repository Information - part 1Entities (from ER diagram)Files (which implement entities)File-to-field relationship (establishes file layout)Fields (from data dictionary)File-to-file relationshipsrelated files that may be joined togetherRelationship validation
اسلاید 39: Client/Server Design Repository Information - part 2Field typeused to permit inheritance from super classesData type (characteristics of field data)File type (used to identify file location)Field function (key, foreign key, attribute, etc.)Allowed valuesBusiness valuesrules for editing, calculating derived fields, etc.
اسلاید 40: Data Distribution and Management Techniques - part 1Relational data base management systemsManual extractuser allowed to manually copy data from server to clientSnapshotautomates manual extract by specifying a copy of the data be transferred from the client to the server at predefined intervals
اسلاید 41: Data Distribution and Management Techniques - part 2Replicationmultiple copies of data are maintained at different sitesFragmentationsystem database is spread across several machines
اسلاید 42: Client/Server Design Approach1. For each elementary business process, identify the files created, updated, referenced, or deleted.2. Use files from step 1 as basis for defining components.3. For each component, retrieve the business rules and other business object information that has been established for the relevant file.4. Determine which rules are relevant to the process and decompose the rules down to the method level.5. As required, define any additional components that are needed to implement the methods.
اسلاید 43: Process Design Entities - part 1Methodsdescribe how a business rule is to be implmementedElementary processesbusiness processes identified in the analysis modelProcess/component linkidentifies components that makeup the solution for an elementary business process
اسلاید 44: Process Design Entities - part 2Componentsdescribes components shown on structure chartBusiness rule/component linkidentifies components significant to implementation of a given business rule
اسلاید 45: Client/Server Testing Strategy part 1Application function testsclient applications tested in stand alone mannerServer teststest coordination and management functions of server also measure performance of serverDatabase testscheck accuracy and integrity server dataexamine transactions posted by client, test archiving
اسلاید 46: Client/Server Testing Strategy part 2Transaction testingensure each class of transactions is processed correctlyNetwork communication testingverify communication among network nodes
اسلاید 47: Client/Server Testing TacticsBegins with testing in the small and then proceeds to integration testing using the non-incremental or big bang approachRequires special attention to configuration testing and compatibility testing OO testing tactics can be used for C/S systemsGUI testing requires special techniques in C/S systems (e.g. structured capture/playback)
اسلاید 48: Distributed Object ArchitecturesNo distinctions made between client objects and server objectsEach distributable entity is an object that both provides and consumes servicesObject communication is though an object request broker (middleware or software bus)More complex to design than client/server systems
اسلاید 49: Distributed Object Architecture from Sommerville
اسلاید 50: Distributed Object Architecture AdvantagesAllows system designer to delay decisions on where and how services should be providedVery open architecture that allows new resources to be added as requiredSystem is flexible and scalableDynamic reconfiguration is possible by allowing objects to migrate across the network as required
اسلاید 51: Uses of Distributed Object ArchitecturesAs a logical model that allows you to structure and organize the systemthink about how to provide application functionality solely in terms of services and combinations of servicesAs a flexible approach to the implementation of client/server systemsthe logical model of the system is client/server with both clients and servers realized as distributed object communicating through a software bus
اسلاید 52: Data Mining System Example from Sommerville
اسلاید 53: CORBAInternational standard for an Object Request Broker (e.g. middleware) to manage distributed object communicationLargely platform and language independent (by having versions for several OO environments)DCOM is Microsoft’s alternative approach (but it is highly platform dependent)
اسلاید 54: CORBA ServicesNaming and trading servicesallow object to discover and refer to other objects on the networkNotification servicesallow objects to notify each other when events have occurredTransaction servicessupport atomic transactions and rollback on failure
اسلاید 55: CORBA Application Structure from Sommerville
اسلاید 56: CORBA StandardsProvides a model for application objectsCOBRA objects encapsulate a state with a well-defined, language neutral interfaceA single object request broker that manages requests for object servicesA set of object services that may be of use to many distributed applicationsA set of common components built on top of these services
اسلاید 57: Object Request Broker (ORB)Handles object communicationsKnows about all system objects and their interfacesUsing the ORB a client object binds an IDL (interface definition language) stub and defines the interface of the server objectCalling the stub results in calls to the ORB which calls the required object through a published IDL skeleton that links the interface to the service implementation
اسلاید 58: ORB-based Communications from Sommerville
اسلاید 59: Inter-ORB CommunicationsORB’s are not usually separate programsORB’s are usually linked object libnrariesORB’s handle communication between objects executing on the same machineEach computer in a distributed system may have its own ORBInter-ORB communication is used to handle distributed object calls
اسلاید 60: Inter-ORB Communications from Sommerville
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