Chapter 10

1. Chapter 10 Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Sixth Edition, Rob and Coronel

2. In this chapter, you will learn: • What a distributed database management system (DDBMS) is and what its components are • How database implementation is affected by different levels of data and process distribution • How transactions are managed in a distributed database environment • How database design is affected by the distributed database environment Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

3. 10.1 The Evolution of Distributed Database Management Systems • Distributed database management system (DDBMS) • Governs storage and processing of logically related data over interconnected computer systems in which both data and processing functions are distributed among several sites Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

4. The Evolution of Distributed Database Management Systems (continued) • Centralized database required that corporate data be stored in a single central site • Dynamic business environment and centralized database’s shortcomings (i.e. fell short when quickly moving events required faster response times and equally quick access to information) spawned a demand for applications based on data access from different sources at multiple locations Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

5. Centralized Database Management System What was needed was quick, un-structured access to databases, using ad hoc queries to generate on-the-spot information Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

6. Social and Technological Changes in 1980’s that affected database development an design • Business operations become more decentralizedgeographically • Competition increased at the global level • Customer demands and market needs favored a decentralizedmanagement style • Rapid technological change of low-cost microcomputers. Corporations adopted LAN (Local Area Network) as the basis of their computerized solutions. • The large number of applications based on DBMSs and the need to protect investments in centralized DBMS software made the notion of data sharing attractive Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

7. Social and Technological Changes in 1980’s that affected database development an design • Two database requirements became obvious in 1980’s: • Rapid ad hoc data access • Decentralized multiple-access and multiple-location databases • The factors in 1980’s were even more firmly entrenched in 1990’s by: • The growing acceptance of Internet as the platform for data access and distribution • The increased focus on data analysis that led to data mining and data warehouse Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

8. Problems of Centralized Database Management • Performance degradation due to a growing number of remote locations over greater distances • High costs associated with maintaining and operating large central database systems • Reliability problems created by dependence on a central site Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

9. 10.2 DDBMS Advantages • Data are located near “greatest demand” site • Faster data access • Faster data processing: able to process data at several sites, spreading out the system’s workload • Growth facilitation • Improved communications • Reduced operating costs • User-friendly interface • Less danger of a single-point failure • Processor independence Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

10. 10.3 DDBMS Disadvantages • Complexity of management and control • Security • Lack of standards • transaction management, concurrency control, security, backup, recovery, query optimization, access path selection, etc. • Increased storage requirements • Greater difficulty in managing the data environment • Increased training cost Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

11. 10.4 Distributed Processing and Distributed Databases A database’s logical processing is shared among several physically independent sites connected through a network Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

12. Distributed Database Environment Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

13. 10.5 Characteristics of Distributed Database Management Systems • A DDBMS must have at least the following functions • Application interface • Validation to analyze data requests • Transformation to determine which request components are distributed and which are local • Query optimization • Mapping • I/O interface • Formatting • Security • Backup and recovery • DB administration • Concurrency control • Transaction management Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

14. Characteristics of Distributed Management Systems (continued) • Must perform all the functions of a centralized DBMS • Must handle all necessary functions imposed by the distribution of data and processing • Must perform these additional functions transparently(透通)to the end user • Receive an application’s request • Validate, analyze, and decompose the request • Map the request’s logical-to-physical data components • Decompose the request into several disk I/O operations • Search for, locate, read, and validate the data • Ensure database consistency, security, and integrity • Validate the data for the conditions specified by the request • Present the selected data in the required format Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

15. A Fully Distributed Database Management System Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

16. 10.6 DDBMS Components • Must include (at least) the following components: • Computer workstations • Network hardware and software • Communications media • Transaction processor (or, application processor, or transaction manager) • Software component found in each computer that requests data. It receives and processes the application’s data requests (remote and local). • Data processor or data manager • Software component residing on each computer that stores and retrieves data located at the site • May be a centralized DBMS Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

17. Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

18. Communication among TPs and DPs • Communication among TPs and DPs is through a specific set of protocols used by the DDBMS. The protocols determine how the DDBMS will: • Interface the network to transport data and commands between DPs and TPs • In TP, synchronize all data received from DPs • In DP, route retrieved data to the appropriate TPs • Ensure common DB functions in a distributed system Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

19. 10.7 Levels of Data and Process Distribution Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

20. Single-Site Processing, Single-Site Data (SPSD) • All processing is done on single CPU or host computer (mainframe, midrange, or PC) • All data are stored on host computer’s local disk • Processing cannot be done on end user’s side of the system • Typical of most mainframe and midrange computer DBMSs • DBMS is located on the host computer, which is accessed by dumb terminals connected to it • Also typical of the first generation of single-user microcomputer databases Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

21. Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

22. Multiple-Site Processing, Single-Site Data (MPSD) • Multiple processes run on different computers sharing a single data repository • MPSD scenario requires a network file server running conventional applications that are accessed through a LAN • Many multi-user accounting applications, running under a personal computer network, fit such a description Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

23. Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

24. Multiple-Site Processing, Single-Site Data • TP acts as a redirector to route all data requests to the file server • The end user sees the file server as just another hard disk • The end user must make a direct reference to the file server to access remote data • All data selection, search, and update functions take place at the workstation, thus requiring the entire file travel through the network for processing at the workstation • A variation is known as Client/Server architecture • Alldatabase processing is done at the server site, thus reducing the network traffic Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

25. Multiple-Site Processing, Multiple-Site Data (MPMD) • Fully distributed database management system with support for multiple data processors and transaction processors at multiple sites • Classified as either homogeneous or heterogeneous • Homogeneous DDBMSs • Integrate only one type of centralized DBMS over a network Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

26. Multiple-Site Processing, Multiple-Site Data (MPMD) (continued) • Heterogeneous DDBMSs • Integrate different types of centralized DBMSs over a network • Fully heterogeneous DDBMS • Support different DBMSs that may even support different data models (relational, hierarchical, or network) running under different computer systems, such as mainframes and microcomputers Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

27. Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

28. Example Restrictions for Heterogeneous DDBMS • Remote access is read-only and does not support write privileges • Restricted number of remote tables that may be accessed in a single transaction • Restricted number of distinct databases that may be accessed • Restrictions on the database model that may be accessed. • And others Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel