The Advantages and Disadvantages of DDBMS
There are several Advantages and disadvantages of DDBMS.
Advantages of DDBMS are as follows:
1. Data are located near the greatest demand site. The data in a distributed database system are dispersed to match business requirements which reduce the cost of data access.
2. Faster data access. End users often work with only a locally stored subset of the company’s data.
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3. Faster data processing. A distributed database system spreads out the systems workload by processing data at several sites.
4. Growth facilitation. New sites can be added to the network without affecting the operations of other sites.
5. Improved communications. Because local sites are smaller and located closer to customers, local sites foster better communication among departments and between customers and company staff.
6. Reduced operating costs. It is more cost-effective to add workstations to a network than to update a mainframe system. Development work is done more cheaply and more quickly on low-cost PCs than on mainframes.
7. User-friendly interface. PCs and workstations are usually equipped with an easy-to-use graphical user interface (GUI). The GUI simplifies training and use for end users.
8. Less danger of a single-point failure. When one of the computers fails, the workload is picked up by other workstations. Data are also distributed at multiple sites.
9. Processor independence. The end user is able to access any available copy of the data, and an end user's request is processed by any processor at the data location.
Disadvantages of DDBMS:
1. Complexity of management and control. Applications must recognize data location, and they must be able to stitch together data from various sites. Database administrators must have the ability to coordinate database activities to prevent database degradation due to data anomalies.
2. Technological difficulty. Data integrity, transaction management, concurrency control, security, backup, recovery, query optimization, access path selection, and so on, must all be addressed and resolved.
3. Security. The probability of security lapses increases when data are located at multiple sites. The responsibility of data management will be shared by different people at several sites.
4. Lack of standards. There are no standard communication protocols at the database level. (Although TCP/IP is the de facto standard at the network level, there is no standard at the application level.) For example, different database vendors employ different—and often incompatible—techniques to manage the distribution of data and processing in a DDBMS environment.
5. Increased storage and infrastructure requirements. Multiple copies of data are required at different sites, thus requiring additional disk storage space.
6. Increased training cost. Training costs are generally higher in a distributed model than they would be in a centralized model, sometimes even to the extent of offsetting operational and hardware savings.
7. Costs. Distributed databases require duplicated infrastructure to operate (physical location, environment, personnel, software, licensing, etc.)
Characteristics of Distributed Database Management Systems:
A 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. A DBMS must have at least the following functions to be classified as distributed:
• Application interface to interact with the end user, application programs, and other DBMSs within the distributed database.
• Validation to analyze data requests for syntax correctness.
• Transformation to decompose complex requests into atomic data request components.
• Query optimization to find the best access strategy. (Which database fragments must be accessed by the query, and how must data updates, if any, be synchronized?)
• Mapping to determine the data location of local and remote fragments.
• I/O interface to read or write data from or to permanent local storage.
• Formatting to prepare the data for presentation to the end user or to an application program.
• Security to provide data privacy at both local and remote databases.
• Backup and recovery to ensure the availability and recoverability of the database in case of a failure.
• Backup and recovery to ensure the availability and recoverability of the database in case of a failure.
• DB administration features for the database administrator.
• DB administration features for the database administrator.
• Concurrency control to manage simultaneous data access and to ensure data consistency across database fragments in the DDBMS.
• Concurrency control to manage simultaneous data access and to ensure data consistency across database fragments in the DDBMS.
• Transaction management to ensure that the data moves from one consistent state to another. This activity includes the synchronization of local and remote transactions as well as transactions across multiple distributed segments.
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