1. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 1 Models of Software Architectures

2. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 2 Objectives (Chapter 12) l To explain the advantages and disadvantages of different distributed systems architectures l To discuss client-server and distributed object architectures l To describe object request brokers and the principles underlying the CORBA standards l To introduce peer-to-peer and service-oriented architectures as new models of distributed computing.

3. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 3 Objectives (Chapter 13) l To explain the organisation of two fundamental models of business systems - batch processing and transaction processing systems l To describe the abstract architecture of resource management systems l To explain how generic editors are event processing systems l To describe the structure of language processing systems

4. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 4 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

5. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 5 Use of architectures l As a starting point for architectural design. l As a design checklist. l As a way of organising the work of the development team. l As a means of assessing components for reuse. l We will examine some important architectural models from two perspectives: Distribution strategy – how subsystems are decomposed and distributed over several computers Application types – how subsystems are decomposed based on application-specific functionality

6. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 6 Computer systems l Personal systems that are not distributed and that are designed to run on a personal computer or workstation. l Embedded systems that run on a single processor or on an integrated group of processors. l Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network.

7. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 7 Distributed systems l Information processing is distributed over several computers rather than confined to a single machine. l Virtually all large computer-based systems are now distributed systems. l Distributed software engineering is therefore very important for enterprise computing systems.

8. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 8 Distributed system characteristics l Resource sharing Sharing of hardware and software resources. l Openness Use of equipment and software from different vendors. l Concurrency Concurrent processing to enhance performance. l Scalability Increased throughput by adding new resources. l Fault tolerance The ability to continue in operation after a fault has occurred.

9. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 9 Distributed system disadvantages l Complexity Typically, distributed systems are more complex than centralised systems. l Security More susceptible to external attack. l Manageability More effort required for system management. l Unpredictability Unpredictable responses depending on the system organisation and network load.

10. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 10 Intra-organizational distributed systems architectures l Client-server architectures Distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services. l Distributed object architectures No distinction between clients and servers. Any object on the system may provide and use services from other objects.

11. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 11 Middleware l Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system. l Middleware is usually off-the-shelf rather than specially written software. l Examples Transaction processing monitors; Data converters; Communication controllers.

12. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 12 Multiprocessor architectures l Simplest distributed system model. l System composed of multiple processes which may (but need not) execute on different processors. l Architectural model of many large real-time systems. l Distribution of process to processor may be pre-ordered or may be under the control of a dispatcher.

13. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 13 A multiprocessor traffic control system

14. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 14 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

15. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 15 Client-server architectures l The application is modelled as a set of services that are provided by servers and a set of clients that use these services. l Clients know of servers but servers need not know of clients. l Clients and servers are logical processes l The mapping of processors to processes is not necessarily 1 : 1.

16. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 16 A client-server system

17. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 17 Computers in a C/S network

18. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 18 Layered application architecture l Presentation layer Concerned with presenting the results of a computation to system users and with collecting user inputs. l Application processing layer Concerned with providing application specific functionality e.g., in a banking system, banking functions such as open account, close account, etc. l Data management layer Concerned with managing the system databases.

19. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 19 Application layers

20. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 20 Thin and fat clients l Thin-client model In a thin-client model, all of the application processing and data management is carried out on the server. The client is simply responsible for running the presentation software. l Fat-client model In this model, the server is only responsible for data management. The software on the client implements the application logic and the interactions with the system user.

21. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 21 Thin and fat clients

22. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 22 Thin client model l Used when legacy systems are migrated to client server architectures. The legacy system acts as a server in its own right with a graphical interface implemented on a client. l A major disadvantage is that it places a heavy processing load on both the server and the network.

23. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 23 Fat client model l More processing is delegated to the client as the application processing is locally executed. l Most suitable for new C/S systems where the capabilities of the client system are known in advance. l More complex than a thin client model especially for management. New versions of the application have to be installed on all clients.

24. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 24 A client-server ATM system

25. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 25 Three-tier architectures l In a three-tier architecture, each of the application architecture layers may execute on a separate processor. l Allows for better performance than a thin- client approach and is simpler to manage than a fat-client approach. l A more scalable architecture - as demands increase, extra servers can be added.

26. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 26 A 3-tier C/S architecture

27. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 27 An internet banking system

28. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 28 Use of C/S architectures

29. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 29 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

30. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 30 Distributed object architectures l There is no distinction in a distributed object architectures between clients and servers. l Each distributable entity is an object that provides services to other objects and receives services from other objects. l Object communication is through a middleware system called an object request broker. l However, distributed object architectures are more complex to design than C/S systems.

31. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 31 Distributed object architecture

32. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 32 Advantages of distributed object architecture l It allows the system designer to delay decisions on where and how services should be provided. l It is a very open system architecture that allows new resources to be added to it as required. l The system is flexible and scaleable. l It is possible to reconfigure the system dynamically with objects migrating across the network as required.

33. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 33 Uses of distributed object architecture l As a logical model that allows you to structure and organise the system. In this case, you think about how to provide application functionality solely in terms of services and combinations of services. l As a flexible approach to the implementation of client-server systems. The logical model of the system is a client-server model but both clients and servers are realised as distributed objects communicating through a common communication framework.

34. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 34 A data mining system

35. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 35 Data mining system l The logical model of the system is not one of service provision where there are distinguished data management services. l It allows the number of databases that are accessed to be increased without disrupting the system. l It allows new types of relationship to be mined by adding new integrator objects.

36. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 36 CORBA l CORBA is an international standard for an Object Request Broker - middleware to manage communications between distributed objects. l Middleware for distributed computing is required at 2 levels: At the logical communication level, the middleware allows objects on different computers to exchange data and control information; At the component level, the middleware provides a basis for developing compatible components. CORBA component standards have been defined.

37. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 37 CORBA application structure l Application objects. l Standard objects, defined by the OMG, for a specific domain e.g. insurance. l Fundamental CORBA services such as directories and security management. l Horizontal (i.e. cutting across applications) facilities such as user interface facilities.

38. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 38 CORBA application structure

39. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 39 CORBA standards l An object model for application objects A CORBA object is an encapsulation of state with a well-defined, language-neutral interface defined in an IDL (interface definition language). l An object request broker that manages requests for object services. l A set of general object services of use to many distributed applications. l A set of common components built on top of these services.

40. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 40 CORBA objects l CORBA objects are comparable, in principle, to objects in C++ and Java. l They MUST have a separate interface definition that is expressed using a common language (IDL) similar to C++. l There is a mapping from this IDL to programming languages (C++, Java, etc.). l Therefore, objects written in different languages can communicate with each other.

41. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 41 ORB-based object communications

42. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 42 Object request broker (ORB) l The ORB handles object communications. It knows of all objects in the system and their interfaces. l Using an ORB, the calling object binds an IDL stub that defines the interface of the called object. l Calling this stub results in calls to the ORB which then calls the required object through a published IDL skeleton that links the interface to the service implementation.

43. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 43 Inter-ORB communications l ORBs are not usually separate programs but are a set of objects in a library that are linked with an application when it is developed. l ORBs handle communications between objects executing on the sane machine. l Several ORBS may be available and each computer in a distributed system will have its own ORB. l Inter-ORB communications are used for distributed object calls.

44. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 44 Inter-ORB communications

45. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 45 CORBA services l Naming and trading services These allow objects to discover and refer to other objects on the network. l Notification services These allow objects to notify other objects that an event has occurred. l Transaction services These support atomic transactions and rollback on failure.

46. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 46 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

47. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 47 Inter-organisational computing l For security and inter-operability reasons, most distributed computing has been implemented at the enterprise level. l Local standards, management and operational processes apply. l Newer models of distributed computing have been designed to support inter- organisational computing where different nodes are located in different organisations.

48. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 48 Peer-to-peer architectures l Peer to peer (p2p) systems are decentralised systems where computations may be carried out by any node in the network. l The overall system is designed to take advantage of the computational power and storage of a large number of networked computers. l Most p2p systems have been personal systems but there is increasing business use of this technology.

49. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 49 P2p architectural models l The logical network architecture Decentralised architectures; Semi-centralised architectures. l Application architecture The generic organisation of components making up a p2p application. l Focus here on network architectures.

50. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 50 Decentralised p2p architecture

51. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 51 Semi-centralised p2p architecture

52. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 52 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

53. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 53 Service-oriented architectures l Based around the notion of externally provided services (web services). l A web service is a standard approach to making a reusable component available and accessible across the web A tax filing service could provide support for users to fill in their tax forms and submit these to the tax authorities.

54. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 54 A generic service l An act or performance offered by one party to another. Although the process may be tied to a physical product, the performance is essentially intangible and does not normally result in ownership of any of the factors of production. l Service provision is therefore independent of the application using the service.

55. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 55 Web services

56. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 56 Services and distributed objects l Provider independence. l Public advertising of service availability. l Potentially, run-time service binding. l Opportunistic construction of new services through composition. l Pay for use of services. l Smaller, more compact applications. l Reactive and adaptive applications.

57. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 57 Services standards l Services are based on agreed, XML-based standards so can be provided on any platform and written in any programming language. l Key standards SOAP - Simple Object Access Protocol; WSDL - Web Services Description Language; UDDI - Universal Description, Discovery and Integration.

58. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 58 Services scenario l An in-car information system provides drivers with information on weather, road traffic conditions, local information etc. This is linked to car radio so that information is delivered as a signal on a specific radio channel. l The car is equipped with GPS receiver to discover its position and, based on that position, the system accesses a range of information services. Information may be delivered in the driver’s specified language.

59. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 59 Automotive system

60. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 60 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

61. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 61 Generic application architectures l Application systems are designed to meet an organisational need. l As businesses have much in common, their application systems also tend to have a common architecture that reflects the application requirements. l A generic architecture is configured and adapted to create a system that meets specific requirements. l A generic architecture can be used as a basic vocabulary for talking about application types.

62. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 62 Application types l Data processing applications Data driven applications that process data in batches without explicit user intervention during the processing. l Transaction processing applications Data-centred applications that process user requests and update information in a system database. l Event processing systems Applications where system actions depend on interpreting events from the system’s environment. l Language processing systems Applications where the users’ intentions are specified in a formal language that is processed and interpreted by the system.

63. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 63 Application type examples l Data processing systems Billing systems; Payroll systems. l Transaction processing systems E-commerce systems; Reservation systems. l Event processing systems Word processors; Real-time systems. l Language processing systems Compilers; Command interpreters.

64. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 64 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

65. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 65 Data processing systems l Systems that are data-centred where the databases used are usually orders of magnitude larger than the software itself. l Data is input and output in batches Input: A set of customer numbers and associated readings of an electricity meter; Output: A corresponding set of bills, one for each customer number. l Data processing systems usually have an input-process-output structure.

66. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 66 Input-process-output model

67. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 67 Input-process-output l The input component reads data from a file or database, checks its validity and queues the valid data for processing. l The process component takes a transaction from the queue (input), performs computations and creates a new record with the results of the computation. l The output component reads these records, formats them accordingly and writes them to the database or sends them to a printer.

68. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 68 Data-flow diagrams l Show how data is processed as it moves through a system. l Transformations are represented as round- edged rectangles, data-flows as arrows between them and files/data stores as rectangles.

69. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 69 Salary payment DFD

70. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 70 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

71. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 71 Transaction processing systems l Process user requests for information from a database or requests to update the database. l From a user perspective a transaction is: Any coherent sequence of operations that satisfies a goal; For example - find the times of flights from London to Paris. l Users make asynchronous requests for service which are then processed by a transaction manager. l Transaction processing systems are often also client-server systems.

72. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 72 Transaction processing

73. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 73 ATM system organisation

74. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 74 ATM client-server architecture

75. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 75 Transaction processing middleware l Transaction management middleware or teleprocessing monitors handle communications with different terminal types (e.g. ATMs and counter terminals), serialises data and sends it for processing. l Query processing takes place in the system database and results are sent back through the transaction manager to the user’s terminal.

76. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 76 ATM transaction management

77. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 77 Information systems architecture l Information systems have a generic architecture that can be organised as a layered architecture. l Layers include: The user interface User communications Information retrieval System database

78. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 78 Information system structure

79. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 79 LIBSYS architecture l The library system LIBSYS is an example of an information system. l User communications layer: LIBSYS login component; Form and query manager; Print manager; l Information retrieval layer Distributed search; Document retrieval; Rights manager; Accounting.

80. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 80 LIBSYS organisation

81. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 81 Resource allocation systems l Systems that manage a fixed amount of some resource (football game tickets, books in a bookshop, etc.) and allocate this to users. l Examples of resource allocation systems: Timetabling systems where the resource being allocated is a time period; Library systems where the resource being managed is books and other items for loan; Air traffic control systems where the resource being managed is the airspace.

82. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 82 Resource allocation architecture l Resource allocation systems are also layered systems that include: A resource database; A rule set describing how resources are allocated; A resource manager; A resource allocator; User authentication; Query management; Resource delivery component; User interface.

83. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 83 Layered resource allocation

84. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 84 Layered system implementation l Each layer can be implemented as a large scale component running on a separate server. This is the most commonly used architectural model for web-based systems. l On a single machine, the middle layers are implemented as a separate program that communicates with the database through its API. l Fine-grain components within layers can be implemented as web services.

85. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 85 E-commerce system architecture l E-commerce systems are Internet-based resource management systems that accept electronic orders for goods or services. l They are usually organised using a multi-tier architecture with application layers associated with each tier.

86. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 86 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

87. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 87 Event processing systems l These systems respond to events in the system’s environment. l Their key characteristic is that event timing is unpredictable so the architecture has to be organised to handle this. l Many common systems such as word processors, games, etc. are event processing systems.

88. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 88 Editing systems l Real-time systems (Chapter 15) and editing systems are the most common types of event processing system. l Editing system characteristics: Single user systems; Must provide rapid feedback to user actions; Organised around long transactions so may include recovery facilities.

89. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 89 Editing system architecture

90. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 90 Editing system components l Editing systems are naturally object-oriented: Screen - monitors screen memory and detects events; Event - recognises events and passes them for processing; Command - executes a user command; Editor data - manages the editor data structure; Ancillary data - manages other data such as styles and preferences; File system - manages file I/O; Display - updates the screen display.

91. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 91 Topics covered l Distributed architectures (Chapter 12) Client-server architectures Distributed object architectures Peer-to-peer architectures Service-oriented architectures l Application architectures (Chapter 13) Data processing systems Transaction processing systems Event processing systems Language processing systems

92. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 92 Language processing systems l Accept a natural or artificial language as input and generate some other representation of that language. l May include an interpreter to act on the instructions in the language that is being processed. l Used in situations where the easiest way to solve a problem is to describe an algorithm or describe the system data Meta-case tools process tool descriptions, method rules, etc and generate tools.

93. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 93 A language processing system

94. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 94 Language processing components l Lexical analyser l Symbol table l Syntax analyser l Syntax tree l Semantic analyser l Code generator

95. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 95 Data-flow model of a translator

96. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 96 Repository model of a translator

97. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 97 l Architectural models are useful starting points for system design. l In distributed systems, subsystems are distributed over several computers. l Generic models of application architectures help us understand and compare certain types of applications. Key points

98. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 98 l Client-server architectures Involve services being delivered by servers to programs operating on clients. Three layers distributed over client and server: user interface, application processing, data management. l Distributed object architectures No distinction between clients and servers. Require middleware to handle object communications and to add and remove system objects. CORBA – a set of middleware standards. l Peer to peer architectures Decentralised systems where computations may be carried out by any node in the network. l Service-oriented architectures Make a service available externally. Key points

99. Modifed from Sommerville’s originalsSoftware Engineering, 7th edition. Chapter 12 & 13 Slide 99 l Data processing systems Data is input and output in batches. l Transaction processing systems Users interact with the system through atomic data transactions. Includes a transaction management subsystem. l Event processing systems Respond to events in a timely manner. No central controller; critical components respond directly to events. l Language processing systems Process languages (natural or artificial) as input to accomplish some complex data processing function. Includes a translator and an interpreter. Key points