What additional functions does a DDBMS have over a centralized DBMS?

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 Additional functions of DDBMS over Centralized DBMS are as follows:

Keeping track of data: The ability to keep track of the data distribution, fragmentation, and replication by expanding the DDBMS catalog.

Distributed query processing: The ability to access remote sites and transmit queries and data among the various sites via a communication network.

Distributed transaction management: The ability to devise execution strategies for queries and transactions that access data from more than one site and synchronize the access to distributed data and maintain the integrity of the overall database.

Replicated data management: The ability to decide which copy of a replicated data item to access and to maintain the consistency of copies of a replicated data item.

Distributed database recovery: The ability to recover from individual site crashes and from new types of failures such as the failure of communication links.

Security: Distributed transactions must be executed with the proper management of the security of the data and the authorization/access privileges of users.

Distributed directory (catalog) management: A directory contains information (meta-data) about data in the database. The directory may be global for the entire DDB, or local for each site. The placement and distribution of the directory are design and policy issues.



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