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Last updated: Nov. 12,2002 |
SOME MORE ABOUT DDBMS
Objective:
To minimize network utilization i.e. to minimize the number of messages.
Problems associated:
Ø Database design
Ø Query processing
Ø Recovery control
Ø Update propagation
Ø Concurrency control
Ø Catalog management
Ø Deadlock management
Ø Operating system support
Ø Heterogeneous databases
Properties:
§ Distributed data independence - user should not know about the
location of data.
§ Distributed transaction atomicity - there is no difference between
distributed transaction and local transaction
Advantages:
1. Management of distributed data with different levels of transparency. Different
types of transparencies are:
Ø Distributed or network transparency
Ø Replication transparency - makes the user unaware of the existence
of copies.
Ø Fragmentation - makes the user unaware of the fragments.
2. Increased reliability and availability.
Here reliability means the probability that a system is running (not down) at
a certain time point and the availability means the probability that the system
is continuously available during a time interval.
3. Improved performance.
4. Easier expansion.
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Additional functions of DDBMS:
Ø Keep track of data.
Ø Distributed query processing.
Ø Distributed data management.
Ø Distributed database recovery
Ø Distributed transaction management.
Ø Distributed directory (catalog) management.
Ø Security.
Failures in DDBMS:
Ø Media failures
Ø Transaction failures
Ø Site (System) failures
Ø Communication failures.
To learn about the architecture
click here.