ICT OCR A Level - Distributed Databases

What are they?
1. A single logical databse
2. All parts are physically in different locations
3. Parts are accessible over a network.
4. A standard Database looks like:
5. A typical database looks like:
6. Each site has a Database Management System (DBMS)
  1. Allows queries to be made locally
  2. Also has a Distributed Database Management System
    1. Allows queries to be made globally for the whole system
Why use them?
1. Examples of uses:
  1. Travel company with branches across the globe
  2. International car manufacturer
  3. Supermarket stocks with multiple branches
2. Some companies may need information up to date all of the time
  1. Access the data globally once a user has updated the files.
3. Distributed databases reduce the risk of losing work
  1. Central database is updated overnight
    1. Batch processing
  2. If the network goes down, then work is not lost and employees can work as normal until the issues are fixed.
    1. Mainly independant; if one branch goes down, the others aren't affected
Duplicated Databases
1. Local copy of each part of the entire database is kept at each location
2. Not very practical for a number of reasons.
3. Disadvantages.
  1. Very heavy use of the network
  2. Whole database may be large and require a lot of storage space
  3. Difficult to keep all copies up to date simultaneously
  4. Does not scale well if the company grows
  5. Wasteful if only certain parts are needed at certain branches
4. Advantage
  1. More practical if the company is fairly small
Partitioned Databases
1. Database is 'split' or partitioned into different datasets depending on the specific needs of the organisation
2. Advantages
  1. Each data store is independant
  2. Network load is much less
  3. Higher performance since there is no network bottleneck
  4. Easier to solve problems due to each store being independant
  5. Scales up very easily
3. Disadvantages
  1. May not be the best solution if each branch needs constant updates of data
  2. Needs to be carefully partitioned to keep each section as local as possible
4. Partitioned+Index
  1. A modification of the partitioned database is to include an index of all remote database records as well
  2. Each store has an index pointing to all records in the entire database
  3. Advantages
    1. Still a high performance as most queries remain local
    2. Can efficiently access remote records by using the index
  4. Disadvantages
    1. System must keep all indexes up to date
    2. More complicated to create and manage
Overall
1. Security
  1. Multiple entry points, this can make the database less secure. Each 'node' needs to be kept secure
  2. Data encryption keys are more likely to be intercepted if they are spread around the organisation constantly
  3. If one node is hacked then the rest of the organisation is vulnerable as well
2. Advantages
  1. Resilient, if one part of the database stops working, there rest are not affected
  2. Security: each employee is able to access one portion of the data
  3. Network traffic is minimised so there is less bandwidth expenses
  4. Easier to keep any errors local
  5. High performance due to less network bottleneck
3. Disadvantages
  1. More complex to create and maintain
  2. Many entry points to the whole database is less secure
  3. Data integrity is harder to maintain to ensure the indexes are not corrupted
  4. Not as effective if there is heavy interaction between branches

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ICT OCR A Level - Distributed Databases

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