So far we have not addressed the problems relating to concurrently accessing a database in a multi-user environment. In the real world single-user databases on microcomputer systems are not adequate to meet the needs of many organisations and companies. Often more than one user may wish to read or update the database simultaneously. This can lead to an inconsistent database. As with any information, if it is not accurate for whatever reason, its value is reduced and it may cause problems for the user. The usefulness of a database system depends on the reliability of its data at all times. For example, a database system which allowed two people to book the same seat on an airline flight, with the resulting confusion and likely customer dissatisfaction, would be of little use indeed, unless of course the airline has a deliberate policy of double booking a certain percentage of seats.
KeywordsDatabase System Data Item Concurrency Control Serialisable Execution Deadlock Prevention
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