111207
Beschreibung
Mindmap von scott.dowle, aktualisiert more than 1 year ago
|
Erstellt von scott.dowle
vor mehr als 11 Jahre
|
|
Distributed Databases
- Database held in different
locations. This is achieved
by:
- Remote processor has data on its
own customers, stock etc. This
database is uploaded each night and
changes made.
- Entire database is
duplicated at the
remote site. Uploaded
each night and
changes made
- Central database contains only
an index of entries. Actual records
held at remote site. Query to the
central database will locate where
record is held. Used for very large
databases.
- Remote processor has data on its
own customers, stock etc. This
database is uploaded each night and
changes made.
- Growing rapidly due to
speed of processing at
local sites has increased
- Data can be
distributed across
multiple computers
- The Internet Domain Name
System (DNS) appears to be
single database used to hold
all addresses in the WWW
- However, Top Level Domains
(.com, .org, .co.uk) split into
different domains stored on
different servers
- However, Top Level Domains
(.com, .org, .co.uk) split into
different domains stored on
different servers
- The Internet Domain Name
System (DNS) appears to be
single database used to hold
all addresses in the WWW
- Distributed database
consists of two or more
data files at different sites
on the network.
- Different users can access it
without interfering with one
another. However, data must be
periodically synchronised to
ensure data consistency
- Different users can access it
without interfering with one
another. However, data must be
periodically synchronised to
ensure data consistency
- Local Systems often
store local databases
but still have access to
central online database
- Central database
accessed remotley or
held on local machines.
- A system is needed to ensure
that data integrity is
maintained by ensuring the
database is updated.
- A system is needed to ensure
that data integrity is
maintained by ensuring the
database is updated.
- Central database
accessed remotley or
held on local machines.
- Advantages
- Faster response
times and service at
each location
- Reduce vulnerability
of putting all
essential data at one
site
- Faster response
to local queries
- Reduction in amount of network traffic
- Effect of
breakdowns
minimized
- Better local control
- Less powerful
cheaper
processors
needed
- Faster response
times and service at
each location
- Limitations
- Security - dependence on
telecommuncaitions links
and widening access to
sensitive data
- Increased data
redundancy is
replicated database
is chosen
- Inconsistencies can arise between
central and local systems if not
immediately updated
- Increased tendency
to data redundancy
and inconsistency
- System dependant on high
quality telecommunication
lines
- Maintain and enforce
consistent standards and data
definitions over wide area
- Increased security problems - enforces
security procedures over wide area plus
increased problems over data transmission
- Security - dependence on
telecommuncaitions links
and widening access to
sensitive data
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