Ø mimics organisational structure with data
Ø local access and autonomy without exclusion
Ø cheaper to create and easier to expand
Ø improved availability/reliability/performance by removing reliance on a
central site
Ø Reduced communication overhead
§
Most data access is local,
less expensive and performs better
Ø Improved processing power
§
Many machines handling the
database rather than a single server
Ø more complex to implement
Ø more costly to maintain
Ø security and integrity control
Ø standards and experience are lacking
Ø Design issues are more complex
1.2 DISTRIBUTED
DATABASES ARCHITECTURE
Ø Defines the structure of the system
o
components
identified
o
functions
of each component defined
o
interrelationships
and interactions between components defined
What is a distributed database?
l“A logically interrelated
collection of shared data (and a description of this data), physically distributed over a computer
network”
Implicit Assumptions
Ø Data stored at a
number of sites ï each site logically
consists of a single processor.
Ø Processors at
different sites are interconnected by a computer network ï no multiprocessors
o parallel database
systems
Ø Distributed
database is a database, not a collection of files ï data logically
related as exhibited in the users’ access patterns
o relational data
model
Ø D-DBMS is a
full-fledged DBMS
o not remote file
system, not a TP system
Advantages of distributed databases
Ø Capacity and incremental growth
Ø Increase reliability and availability
Ø Modularity
Ø Reduced communication overhead
Ø Protection of valuable data
Ø Efficiency and Flexibility
Disadvantages
of distributed databases
Ø DDB design more complex, fragmentation & replication; extra work
must be done by the DBAs to ensure that the distributed nature of the
system is transparent.
Ø Economics,
Ø Concurrency control,
Ø Inexperience,
Ø Security,
Ø Difficult to maintain integrity
Applications
Ø
Manufacturing
- especially multi-plant manufacturing
Ø
Military
command and control
Ø
Electronic
fund transfers and electronic trading
Ø
Corporate
MIS
Ø
Airline
restrictions
Ø
Hotel
chains
Ø
Any
organization which has a decentralized organization structure
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