DDBMS has many advantages. Data is located near the greatest demand site, access is faster, processing is faster due to several sites spreading out the work load, new sites can be added quickly and easily, communication is improved, operating costs are reduced, it is user friendly, there is less danger of a single-point failure, and it has process independence.
Several reasons why businesses and organizations move to distributed databases include organizational and economic reasons, reliable and flexible interconnection of existing database, and the future incremental growth. Companies believe that a decentralized, distributed data database approach will adapt more naturally with the structure of the organizations. Distributed database is more suitable solution when several database already exist in an organization. In addition, the necessity of performing global application can be easily perform with distributed database. If an organization grows by adding new relatively independent organizational units, then the distributed database approach support a smooth incremental growth.
Data can physically reside nearest to where it is most often accessed, thus providing users with local control of data that they interact with. This results in local autonomy of the data allowing users to enforce locally the policies regarding access to their data.
One might want to consider a parallel architecture is to improve reliability and availability of the data in a scalable system. In a distributed system, with some careful tact, it is possible to access some, or possibly all of the data in a failure mode if there is sufficient data replication.
DDBMS also has a few disadvantages. Managing and controlling is complex, there is less security because data is at so many different sites.
Distributed databases provides more flexible accesses that increase the chance of security violations since the database can be accessed throughout every site within the network. For many applications, it is important to provide secure. Present distributed database systems do not provide adequate mechanisms to meet these objectives. Hence the solution requires the operation of DDBMS capable of handling multilevel data. Such a system is also called a multi level security distributed database management systems (MLS-DDBMS). MLS-DDBMS provides a verification service for users who wish to share data in the database at different level security. In MLS- DDBMS, every data item in the database has correlated with one of several classifications or sensitivities.
The ability to ensure the integrity of the database in the presence of unpredictable failures of both hardware and software components is also an important features of any distributed database management systems. The integrity of a database is concerned with its consistency, correctness, validity, and accuracy. The integrity controls must be built into the structure of software, databases, and involved personnel.
If there are multiple copies of the same data, then this duplicated data introduces additional complexity in ensuring that all copies are updated for each update. The notion of concurrency control and recoverability consume much of the research efforts in the area of distributed database theory. Increasing in reliability and performance is the goal and not the status quo.