Distribution basically leads to increased complexity in the system design and implementation. This is to achieve the potential advantages such as:
- Network Transparencies
- Increased Reliability
- Improved Performance
- Easier Expansion
Function of Centralized DBMS:
- The basic function of centralized DBMS is that it provides complete view of our data.
For example, we can have the query for the number of customers who are willing to buy worldwide.
- The second basic function of Centralized DBMS is that it is easy to manage than other distributed systems.
The Distributed Database must be able to provide the following function in addition to those of a centralized DBMS’s.
Functions of Distributed database system:
- Keeping track of data –
The basic function of DDBMS is to keep track of the data distribution, fragmentation and replication by expanding the DDBMS catalog.
- Distributed Query Processing –
The basic function of DDBMS is basically its ability to access remote sites and to transmits queries and data among the various sites via a communication network.
- Replicated Data Management –
The basic function of DDBMS is basically to decide which copy of a replicated data item to access and to maintain the consistency of copies of replicated data items.
- Distributed Database Recovery –
The ability to recover from the individual site crashes and from new types of failures such as failure of communication links.
- Security –
The basic function of DDBMS is to execute Distributed Transaction with proper management of the security of the data and the authorization/access privilege of users.
- Distributed Directory Management –
A directory basically contains information 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 may have design and policy issues.
- Distributed Transaction Management –
The basic function of DDBMS is its ability to devise execution strategies for queries and transaction that access data from more than one site and to synchronize the access to distributed data and basically to maintain the integrity of the complete database.
But These function basically increases the complexity of a DDBMS over centralized DBMS.