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Chapter 12

Chapter 12. Distributed Database Management Systems. Let us ponder…. “So what is a Distributed Database…sounds like a Disturbing Database!” “So why would anyone want to have a Distributed Database, anyway!” So, how does it work – this fancy DDB?”. What is Distributed Database?.

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Chapter 12

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  1. Chapter 12 Distributed Database Management Systems

  2. Let us ponder….. “So what is a Distributed Database…sounds like a Disturbing Database!” “So why would anyone want to have a Distributed Database, anyway!” So, how does it work – this fancy DDB?”

  3. What is Distributed Database?

  4. Wotz the difference? Centralised Database vs Distributed Database

  5. CDB v DDB

  6. So wotz the difference? So then is there a difference between “Distributed processing” and “Distributed database”?

  7. Distributed Processing vs DDB Shares database’s logical processing among physically, networked independent sites Stores logically related database over physically independent sites

  8. Ja well no fine So what have we got here with all this centralised, distributed processing, distributed database……?

  9. Levels of Data and Process Distribution Database systems can be classified based on process distribution and data distribution Table 10.1

  10. Single-Site Processing, Single-Site Data (SPSD) • All processing on single CPU or host computer • All data are stored on host computer disk • DBMS located on the host computer • DBMS accessed by dumb terminals • Typical of mainframe and minicomputer DBMSs • Typical of 1st generation of single-user microcomputer database

  11. Single-Site Processing, Single-Site Data Figure 10.6

  12. Multiple-Site Processing, Single-Site Data (MPSD)

  13. Multiple-Site Processing, Single-Site Data (MPSD) • Requires network file server • Applications accessed through LAN • Variation known as client/server architecture

  14. Multiple-Site Processing, Multi Data (MPMD)

  15. Multiple-Site Processing, Multiple-Site Data (MPMD) • Fully distributed DDBMS with support for sites

  16. Too easy OK, so then the Database is at all the sites, the processing takes place at all the sites….Ummm… Do all the sites have the same type of database? Huh?

  17. Homogeneous vs Heterogeneous DDB • Homogeneous • Integrate one type of centralized DBMS over the network • Heterogeneous • Integrate different types of centralized DBMSs over a network No kidding……

  18. Heterogeneous Distributed Database Scenario Gasp! Figure 10.8

  19. So why? “So why would anyone want to have a Distributed Database, anyway!”

  20. DDBMS Advantages • Two main reasons • Speed • Data located near site with greatest demand • Multiple/Parallel processing • Reliability • Improved communications • Redundant copies – no single point failure Yeah…but surely it’s not all roses

  21. DDBMS Disadvantages • Two main thorns • Complex • Setup • Management • Security & Control • Remote data • Data communications

  22. So How? So, how does it work – this fancy DDB?”

  23. DDBMS Components • Computer workstations • Network hardware and software components • Communications media • Transaction processor (TP) • Also called application manager (AP) or transaction manager (TM) • Data processor (DP) • Also called data manager (DM)

  24. Distributed Database Components Figure 10.5

  25. The clever bit is…. The important part is what is invisible….. Distributed DB Transparency

  26. Distributed DB Transparency • Allows end users to feel like only database user • Hides complexities of distributed database • Transparency features • Location • Fragmentation • Heterogeneity • etc

  27. Distributed Transaction Figure 10.12

  28. The hard bit… is Concurrency Control is Query Optimisation is Integrity/Standards Control is Security Controls

  29. Date’s 12 Commandments for Distributed Databases 1. Local Site Independence 2. Central Site Independence 3. Failure Independence 4. Location Transparency 5. Fragmentation Transparency 6. Replication Transparency

  30. Date’s 12 Commandments for Distributed Databases 7. Distributed Query Processing 8. Distributed Transaction Processing 9. Hardware Independence 10. Operating System Independence 11. Network Independence 12. Database Independence

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