DISTRIBUTED DATABASES

Definition

A distributed database has data stored on a number of computers at different locations (1) but appears as one logical database (1).

OR

A distributed database is a single database that is under the control of a DBMS where the storage devices are not all attached to a common processor (1). Instead the data is stored in storage devices attached to multiple computers usually located across a network (1). Or A distributed database has data stored on a number of computers at different locations (1) but appears as one logical database (1).

Advantages

• If data lost on central site it could be reduplicated from local site.

• Allows sharing of the data and the results of processing the data.

• New locations (shops) can be added to the database without the need for rewriting the entire database.

• Faster response to user queries of the database.

• Non-dependence on one central huge store of data.

• Easy to backup and copy data from one server to another.

• If one server fails then the other servers can be used.

• Reduces network traffic as local queries can be performed using the data on the company’s server.

• Data used locally can be stored locally and network traffic kept to a minimum

Disadvantages

• More complex and consequently cost more to install and maintain

• Increased security risk because files are transferred across the network, particularly if sensitive personal data is being transferred

• If one of the servers fails, then it can have an effect on the database and staff may not be able to access some of the data. If one of the links to a server failed then the data could not be obtained from that server.

• The system relies on data communications, so if a communication line fails, then the data may not be able to be accessed

• As large numbers of staff access the access the database, there is a chance that you could get inconsistencies in the data

Application - Hotel Chain

A hotel chain may store details of guests booking on its local network but because each hotel is networked a distributed database can be used and staff in one hotel can see booking in another hotel and managers can monitor booking across the whole chain. Similarly for a chain of shops.

A hotel chain might use distributed databases to store details of reservations. Each hotel stores its own reservations on a local computer.

Case Study - Electronic Patient Records

Research is ongoing on the use of Electronic Patient Records (EPR). This would bring specific benefits to medicine but there would be concerns about its use.

• If you were taken into any hospital anywhere in Britain they could call up your notes and see if you are, for example, on any medication at the moment. This can only lead to
  better diagnosis of patient’s problems and improve the chances of survival.

• The computerising of the patient records would also create a huge database of all the people in Britain. This could also allow an epidemiological investigation to take place. People’s records could be compared to see what treatment worked and what other factors there may have been for some complex illness. Trends could be spotted at their
  early stage and remedial action taken to stop them quickly. This information would be available no matter where the hospital was or what the condition of it is.

• A database such as this can also be seen as a step towards a national identity programme where to get treatment one would have to have proof of nationality and proof of residence in this country. You would have to exist on the database before you could be dealt with. Immigrants, legal or otherwise would have to prove their adherence to these rules.

• The main concern is big brother watching you or the danger of someone getting your data (hacking) and misusing it.

Problems that could arise when using distributed medical databases.

• More complex hence more expensive to install and maintain

• Increased security risk from transfer

• If one location fails might hinder others

• Could get data inconsistency