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Saturday, November 24, 2007

SPSD (Single-site processing)

The Evolution of Distributed DBMS
4 Centralized DBMS in the 1970’s
u Regularly issued formal reports in standard formats.
u Prepared by specialist using 3GL in response to precisely channeled request.
u Centrally stored corporate data.
u Data access through dumb terminals.
u Incapable of providing quick, unstructured, and ad hoc information for decision makers in a dynamic business environment.

The Evolution of Distributed DBMS
4 Social and Technical Changes in the 1980’s
u Business operations became more decentralized geographically.
u Competition increased at the global level.
u Customer demands and market needs favored a decentralized management style.
u Rapid technological change created low-cost microcomputers. The LANs became the basis for computerized solutions.
u 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.

The Evolution of Distributed DBMS
4 Two Database Requirements in a Dynamic Business Environment:
u Quick ad hoc data access became crucial in the quick-response decision making environment.
u The decentralization of management structure based on the decentralization of business units made decentralized multiple-access and multiple-location databases a necessity.
4 Developments in the 1990’s affecting DBMS
u The growing acceptance of the Internet and the World Wide Web as the platform for data access and distribution.
u The increased focus on data analysis that led to data mining and data warehousing.

The Evolution of Distributed DBMS
4 DDBMS Advantages
u Data are located near the “greatest demand” site.
u Faster data access
u Faster data processing
u Growth facilitation
u Improved communications
u Reduced operating costs
u User-friendly interface
u Less danger of a single-point failure
u Processor independence
4 DDBMS Disadvantages
u Complexity of management and control
u Security
u Lack of standards
u Increased storage requirements

Distributed Processing
and Distributed Database
4 Distributed processing shares the database’s logical processing among two or more physically independent sites that are connected through a network.

4 Distributed database stores a logically related database over two or more physically independent sites connected via a computer network.

Distributed Processing
and Distributed Database
4 Distributed processing does not require a distributed database, but a distributed database requires distributed processing.
4 Distributed processing may be based on a single database located on a single computer. In order to manage distributed data, copies or parts of the database processing functions must be distributed to all data storage sites.
4 Both distributed processing and distributed databases require a network to connect all components.

What Is A Distributed DBMS?
4 A distributed database management system (DDBMS) governs the storage and processing of logically related data over interconnected computer systems in which both data and processing functions are distributed among several sites.

What Is A Distributed DBMS?
4 Functions of a DDBMS
u Application interface
u Validation to analyze data requests
u Transformation to determine request’s components
u Query-optimization to find the best access strategy
u Mapping to determine the data location
u I/O interface to read or write data
u Formatting to prepare the data for presentation
u Security to provide data privacy
u Backup and recovery
u Database administration
u Concurrency control
u Transaction management

DDBMS Components
4 Computer workstations that form the network system.
4 Network hardware and software components that reside in each workstation.
4 Communications media that carry the data from one workstation to another.
4 Transaction processor (TP) receives and processes the application’s data requests.
4 Data processor (DP) stores and retrieves data located at the site. Also known as data manager (DM).

Levels of Data & Process Distribution
4 Single-Site Processing, Single-Site Data (SPSD)
u All processing is done on a single CPU or host computer.
u All data are stored on the host computer’s local disk.
u The DBMS is located on the host computer.
u The DBMS is accessed by dumb terminals.
u Typical of most mainframe and minicomputer DBMSs.
u Typical of the 1st generation of single-user microcomputer database.

Levels of Data & Process Distribution
4 Multiple-Site Processing, Single-Site Data (MPSD)
u Typically, MPSD requires a network file server on which conventional applications are accessed through a LAN.
u A variation of the MPSD approach is known as a client/server architecture. (Chapter 12)

Levels of Data & Process Distribution
4 Multiple-Site Processing, Multiple-Site Data (MPMD)
u Fully distributed DBMS with support for multiple DPs and TPs at multiple sites.
l Homogeneous DDMS integrate only one type of centralized DBMS over the network.
l Heterogeneous DDBMS integrate different types of centralized DBMSs over a network. (See Figure 10.8)

Distributed DB Transparency
4 DDBMS transparency features have the common property of allowing the end users to think that he is the database’s only user
 
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