10 Chapter 10 Distributed Database Management Systems Database Systems Design Implementation and Management Fifth Edition Rob and Coronel 10 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 5th Edition Rob Coronel 2 10 Evolution of DDBMS Decentralized database management systems DDBMS Interconnected computer systems Data processing functions reside on multiple sites 1970 s Centralized DBMS Structured information requirements Slow progression from needs to implementation 1980 s Social and Technical Changes Relational model ideal but a resource hog Business and Competitive pressures Ad hoc capability required Decentralized management structure common 1990 s New forces Internet and the World Wide Web used for data access and distribution Data analysis through data mining and data warehousing Database Systems Design Implementation Management 5th Edition Rob Coronel 3 10 Centralized Databases Performance degradation High Costs of mainframe maintenance Reliability All your eggs in one basket Database Systems Design Implementation Management 5th Edition Rob Coronel 4 10 DDBMS Advantages Data located near site with greatest demand Faster data access Faster data processing Growth facilitation Improved communications Reduced operating costs User friendly interface Less danger of single point failure Processor independence Database Systems Design Implementation Management 5th Edition Rob Coronel 5 10 DDBMS Disadvantages Complexity of management and control Applications must recognize data location Synchronization issues Redundancy anomalies Security Lack of standards No application level standards Increased storage requirements Greater difficulty in managing data environment Increased training costs Database Systems Design Implementation Management 5th Edition Rob Coronel 6 10 Distributed Processing Shares database s logical processing among physically networked independent sites file server Figure 10 1 Database Systems Design Implementation Management 5th Edition Rob Coronel 7 10 Distributed Database Stores logically related database over physically independent sites Figure 10 2 Database Systems Design Implementation Management 5th Edition Rob Coronel 8 10 Distributed Database vs Distributed Processing Distributed processing Does not require distributed database May be based on a single database on single computer Copies or parts of database processing functions must be distributed to all data storage sites Distributed database Database fragments Requires distributed processing Both Require a network to connect components Database Systems Design Implementation Management 5th Edition Rob Coronel 9 10 Functions of DDBMS Application end user interface Validation to analyze data requests Transformation to determine request components Query optimization to find the best access strategy Mapping to determine the data location I O interface to read or write data Formatting to prepare the data for presentation Security to provide data privacy Backup and recovery DB Administration Concurrency Control Transaction Management Database Systems Design Implementation Management 5th Edition Rob Coronel 10 10 Centralized Database Figure 10 3 Database Systems Design Implementation Management 5th Edition Rob Coronel 11 Fully Distributed Database Management System 10 Must perform all the functions of a centralized DBMS as well as stitch together the data from many sources transparently Database Systems Design Implementation Management 5th Edition Rob Coronel Figure 10 4 12 10 DDBMS Components Computer workstations Network hardware and software components Communications media Transaction processor TP Receives and processes application requests for data Forwards requests to the Data Processor s Also called application manager AP or transaction manager TM Data processor DP Stores and retrieves data located at a site Also called data manager DM Database Systems Design Implementation Management 5th Edition Rob Coronel 13 10 Distributed Database Components Figure 10 5 Database Systems Design Implementation Management 5th Edition Rob Coronel 14 10 DDBMS Protocols Interface with network to transport data and commands between DPs and TPs Synchronize data received from DPs and route to appropriate TPs Ensure common database functions Security Concurrency control Backup and recovery Database Systems Design Implementation Management 5th Edition Rob Coronel 15 10 Levels of Data and Process Distribution Database systems can be classified based on process distribution and data distribution Table 10 1 Database Systems Design Implementation Management 5th Edition Rob Coronel 16 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 Database Systems Design Implementation Management 5th Edition Rob Coronel 17 10 Single Site Processing Single Site Data con t Figure 10 6 Database Systems Design Implementation Management 5th Edition Rob Coronel 18 10 Multiple Site Processing Single Site Data MPSD TP acts as a redirector Requires network file server Applications accessed through LAN Variation known as client server architecture Figure 10 7 Database Systems Design Implementation Management 5th Edition Rob Coronel 19 10 Multiple Site Processing Multiple Site Data MPMD Fully distributed DDBMS with support for multiple DPs and TPs at multiple sites Homogeneous I Integrate one type of centralized DBMS over the network Heterogeneous Same DBMS Fully Heterogeneous Integrate different types of centralized DBMSs over a network Different OS s Different hardware platforms Database Systems Design Implementation Management 5th Edition Rob Coronel 20 10 Heterogeneous Distributed Database Scenario Figure 10 8 Database Systems Design Implementation Management 5th Edition Rob Coronel 21 10 Fully Hetergeneous Not there yet Those that claim to be Read only Number of table restrictions transaction Number of database restrictions Restriction on the database