This may be done in two ways shared data is held in a

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Sub-systems must exchange data. This may be done in two ways: Shared data is held in a central database or repository and may be accessed by all sub-systems Each sub-system maintains its own database and passes data explicitly to other sub-systems When large amounts of data are to be shared, the repository model of sharing is most commonly used ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 12 CASE toolset architecture Project repository Design translator Program editor Design editor Code generator Design analyser Report generator
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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 13 Repository model characteristics Advantages Efficient way to share large amounts of data Sub-systems need not be concerned with how data is produced. Centralized management e.g. backup, security, etc. Disadvantages Sub-systems must agree on a repository data model, which is inevitably a compromise Data evolution is difficult and expensive No scope for specific management policies Difficult to distribute efficiently ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 14 Client-server architecture Distributed system model which shows how data and processing is distributed across a range of components Set of stand-alone servers which provide specific services such as printing, data management, etc. Set of clients which call on these services Network which allows clients to access servers ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 15 Film and picture library Catalogue server Catalogue Video server Film clip files Picture server Digitized photographs Hypertext server Hypertext web Client 1 Client 2 Client 3 Client 4 Wide-bandwidth network ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 16 Client-server characteristics Advantages Distribution of data is straightforward Makes effective use of networked systems. Easy to add new servers or upgrade existing servers Disadvantages No shared data model so sub-systems use different data organization. data interchange may be inefficient Redundant management in each server No central register of names and services - it may be hard to find out what servers and services are available ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 17 Abstract machine model Used to model the interfacing of sub-systems Organizes the system into a set of layers (or abstract machines) each of which provide a set of services Supports the incremental development of sub- systems in different layers. When a layer interface changes, only the adjacent layer is affected However, often difficult to structure systems in this way ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 18 Version management system Operating system Database system Object management Version management
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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 10 Slide 19 Centralized control
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