What are the advantages and disadvantages of the DDBMS?

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 Advantages of DDBMS

The advantages of DDBS are as follows:

1. Reflects organizational structure: 

Many organizations are naturally distributed over several locations.

2. Improved share-ability and local autonomy: 

The geographical distribution of an organization can be reflected in the distribution of the data; users at one site can access. data stored at other sites. Data can be placed at the site close to the users who normally use that data. In this way, users have local control of the data and they can consequently establish and enforce local policies regarding the use of this data. A global DBA is responsible for the entire system. Generally, part of this responsibility is devolved to the local level, so that the local DBA can manage the local DBMS.

3. Improved availability: 

In a centralized DBMS, a computer failure terminates the operations of the DBMS. However, a failure at one site of a DDBMS or a failure of a communication link making some sites inaccessible does not make the entire system inoperable. Distributed DBMSs are designed to continue to function despite such failures. If a single node fails, the system may be able to reroute the failed node's requests to another site.

4. Improved reliability: 

Because data may be replicated so that it exists at more than one site, the failure of a node or a communication link does not necessarily make the data inaccessible. Improved performance as the data is located near the site of "greatest demand," and given the inherent parallelism of distributed DBMSs, the speed of database access may be better than that achievable from a remote centralized database. Furthermore, since each site handles only a part of the entire database, there may not be the same contention for CPU and I/O services as characterized by a centralized DBMS.

5. Economics: 

The potential cost saving occurs where databases are geographically remote and the applications require access to distributed data. In such cases, owing to the relative expense of data being transmitted across the network as opposed to the cost of local access, it may be much more economical to partition the application and perform the processing locally at each site.

6. Modular growth: 

In a distributed environment, it is much easier to handle expansion. New sites can be added to the network without affecting the operations of other sites. This flexibility allows an organization to expand relatively easily.

7. Integration:

 At the start of this section, we noted that integration was a key advantage of the DBMS approach, not centralization. The integration of legacy systems is one particular example that demonstrates how some organizations are forced to rely on distributed data processing to allow their legacy systems to coexist with their more modern systems. At the same time, no one package can provide all the functionality that an organization requires nowadays. Thus, it is important for organizations to be able to integrate software components from different vendors to meet their specific requirements.

8. Remaining competitive:

There are a number of relatively recent developments that rely heavily on distributed database technology such as e-business, computer-supported collaborative work and workflow management. Many enterprises have had to reorganize their businesses and use distributed database technology to remain competitive.


Disadvantages of DDBMS

The disadvantages of DDBS are as follows:

1. Complexity: 

A distributed DBMS that hides the distributed nature from the user and provides an acceptable level of performance, reliability, and availability is inherently more complex than a centralized DBMS. The fact that data can be replicated also adds an extra level of complexity to the distributed DBMS. If the software does not handle data replication adequately, there will be degradation in availability, reliability, and performance compared with the centralized system, and the advantages we cited earlier will become disadvantages.


2. Cost:

 Increased complexity means that we can expect the procurement and maintenance costs for a DDBMS to be higher than those for a centralized DBMS. Furthermore, a distributed DBMS requires additional hardware to establish a network between sites. There are ongoing communication costs incurred with the use of this network. There are also additional labor costs to manage and maintain the local DBMSs and the underlying network.

3. Security: 

In a centralized system, access to the data can be easily controlled. However, in a distributed DBMS not only does access to replicated data have to be controlled in multiple locations, but the network itself has to be made secure. In the past, networks were regarded as an insecure communication medium. Although this is still partially true, significant developments have been made to make networks more secure.

4. Integrity control more difficult: 

Database integrity refers to the validity and consistency of stored data. Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate. Enforcing integrity constraints generally requires access to a large amount of data that defines the constraint but that is not involved in the actual update operation itself. In a distributed DBMS, the communication and processing costs that are required to enforce integrity constraints may be prohibitive.


5. Lack of standards: 

Although distributed DBMSs depend on effective communication, we are only now starting to see the appearance of standard communication and data access protocols. This lack of standards has significantly limited the potential of distributed DBMSs. There are also no tools or methodologies to help users convert a centralized DBMS into a distributed DBMS.

6. Lack of experience: 

General-purpose distributed DBMSs have not been widely accepted, although many of the protocols and problems are well understood, Consequently, we do not yet have the same level of experience in the industry as we have with centralized DBMSs. For a prospective adopter of this technology, this may be a significant deterrent

7. Database design more complex:

 Besides the normal difficulties of designing a centralized database, the design of a distributed database has to take into account fragmentation of data, allocation of fragments to specific sites, and data replication.



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