Architectural model of distributed system ppt

architectural styles in software architecture ppt and architecture of distributed applications
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Published Date:23-07-2017
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Chapters Chapters 12/31 12/31 Distributed Distributed Systems Systems Architectures & Service-Oriented Software Engineering ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 1Distributed Distributed Systems Systems A Architectures rchitectures Architectural design for software that executes on more than one processor ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 2Service Service-Oriented Oriented Software Software Eng Eng A way of developing distributed systems where the components are stand-alone services. “Currently a hot topic…as important a development as object-oriented software engineering.” (For Chap 31, skip sections: 31.2 and 31.3.1) ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 3zzzzzz Objectives Objectives To To explain explain the the advantages advantages and and disadvantages disadvantages of of distributed systems architectures. To describe different approaches to the development of cli lient-server systems. To explain the differences between client-server and distributed distributed object object architectures architectures. To describe object request brokers and the principles underlying the CORBA standards. To introduce service-oriented SE, an increasingly important approach in business application development. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 4ƒƒ zzzz Topics Topics covered covered Multiprocessing Multiprocessing systems systems Distributed systems architectures Client-server architectures Distributed object architectures CORBA (Common Object Request Broker Architecture) Service-oriented SE ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 5ƒƒ zzzz Topics Topics covered covered Multiprocessing Multiprocessing systems systems Distributed systems architectures Client-server architectures Distributed object architectures CORBA (Common Object Request Broker Architecture) Service-oriented SE ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 6zzzz Multiprocessor Multiprocessor a architectures rchitectures System System composed composed of of multiple multiple process processes es which which may or may not execute on different processors. Distribution Distribution of of process process t to o p processor rocessor may may be be pre pre- determined (e.g., by type of process) or may be under the control of a disp patcher. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 7A multiprocessor traffic control system system Traffic flow Traffic light control Sensor processor processor processor processor processor processor Light Sensor Display control control process process process Traffic lights Traffic flow sensors Operator consoles and cameras ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 11 Slide 8zzzz Types Types o of f m multiprocessing ultiprocessing systems systems Personal Personal systems systems that that are are not not distributed distributed and and that that are designed to run on a personal computer or workstation. (g (e.g.,, word pprocessors) ) Embedded systems that run on a single processor processor or or on on an an integrated integrated group group of of processors processors.. (e.g., control systems, real-time systems) Distributed sy ystems where the sy ystem software runs on a loosely integrated group of processors linked by a network. (e.g., ATM systems) ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 9zzzz Distributed Distributed systems systems Virtually Virtually all all l large, arge, computer computer-based based s systems ystems are now distributed systems. Processing Processing is is distributed distributed over over several several computers computers rather than confined to a single machine. Distributed software enggg ineering is now veryy important. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 10zzzzzzzzz Distributed system characteristics characteristics / / advantages advantages Resource Resource sharing sharing (hardware (hardware and and software) software) Openness (standard protocols allow equipment and software from from different different v vendors endors to to be be combined) combined) Concurrency (parallel processing) Scalability Scalability (up (up to to capacity capacity o of f n network) etwork) Fault tolerance (potential) Transparency Transparency ( (resources resources can can b be e a accessed ccessed w without ithout knowledge knowledge th of their physical or network location – item deleted after 6 Ed.) ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 11zzzzz Distributed Distributed system system disadvantages disadvantages Complexity Complexity (number (number of of factors factors affecting affecting emergent emergent properties) properties) Security (multiple access points, network eavesdropping, etc.) Manageability Manageability (h (het terogeneit ity) ) Unpredictable responsiveness ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 12Design issue Description Resource The resources in a d istributed system are spread across different i id dentifi tificati tion comput tersand d anami ing sch heme ha h s t to bd be devi ised d so t th hat t users can discover and re fer to the resources that they need. An example of such a naming scheme is the URL (Uniform Resource Locator) that is used to identify WWW pages. If a meaningful and universally unde under rs st tood ood i iden denti tif fi ica cati tion on sch schem eme e is is no not t u us sed ed th the en n m many any of of t thes hese e resources will be inaccessible to system users. Communications The universal availability of the Internet and the efficient implementation of Internet TCP/IP communication protocols means that, for most distributed systems, these are the most effective way for the computers to communicate. However, wherethere are specific requirements for performance, reliability etc. alternative approaches to communications may be used. Quality of service The quality of service offered by a system reflects its performance, ava avail ilab abilit ility y a and nd r re eli liab abilit ility y. I It t i isa s af ff fec ect ted ed by by a a nu num mbe ber r o of f f fac act to or rs s su suc ch h as the allocation of processes to processes in the system, the distribution of resources across the system, the network and the system hardware and th e adaptability of the system. Soft f ware The software architecture describes how the app pplication architectures functionality is distributed over a number of logical components and how these components are distributed across processors. Choosing the right architecture for an application is essential to achieve the desired quality of service. Issues in distributed system designzz Distributed Distributed systems systems a architectures rchitectures Client Client-server server architectures architectures – di dist trib ibut ted d services are called on by clients. Servers that provide services are treated differently from clients that use services. Distributed object architectures – removes distinction between clients and servers. Any object in the system may provide and use services from other objects. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 14zzzz Middleware Middleware Software Software that that manages manages and and enables enables commun commun- ication between the diverse components of a distributed sy ystem. Usually off-the-shelf rather than specially written. Distributed system frameworks, e.g. CORBA and DCOM,, is an imp portant class of middle- ware described later. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 15zzzzz Client Client-server server architectures architectures T The hea application pplication is ism modelled odelled as asas a set eto off services services that are provided by servers and a set of clients that use the services. Clients must know of servers but servers need not know of clients. (e.g., “installing” a network printer) Clients and servers are logical processes as opposed to physical machines. The mapping of processors to processes is not necessarily 1:1. ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 16P Processesil in a cliientt-server syst tem c3 c2 c4 c12 c11 Server process Server process c1 s4 s1 c10 c5 c5 Client process s2 s3 c9 c6 c8 c7 ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 17Ct Computers iil n a cliientt-server nettk work c1 c2 c3, c4 CC1 CC2 CC3 Network Server s3, s4 s1, s2 computer SC1 SC1 SC2 SC2 Client computer computer c5, c6, c7 c5, c6, c7 c8, c9 c8, c9 c10, c1 c10, c11, c12 1, c12 CC4 CC5 CC6 ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 18zzz Application Application layers layers model model Presentation Presentation layer layer – concerned d with ith presenting the results of a computation to system implemented users and with collecting user inputs. on on client client only only Application processing layer – concerned with implementing the logic (functionality) of the application. implemented on client or server Data management layer – concerned with all system database operations. implemented on server only ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 19Application Application layers layers Presentation layer Application processing layer layer Data management layer ©Ian Sommerville 2000 Software Engineering. Chapters 12/31 Slide 20

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