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An Investigation Into Database Resilience

Definitions In normal English usage the word resilience is taken to mean the power to resume original shape after compression; in the context of data base management the term data base resilience is defined as the ability to return to a previous state after the occurrence of some event or action which may have changed that state. The particular state of interest is the logical content of a data base. The physical state of the data base may also be of interest if access to the knowledge of this physical state is allowed to application programs. However this knowledge is increasingly denied to application programs in the attempt to preserve data independence (CODASYL, 1971) or to simplify data access by removing the need for navigation (Date and Codd, 1974) and thus returning to a previous logical state is often sufficient. One type of event or action expected is an error in the operation of the system. Hence a particular type of data base resilience of interest is the ability to return to a previous logical data base after the occurrence of an error which may have damaged the logical data base. Terms related to the concept of resilience are: privacy, security and integrity. Privacy is denned as 'whether or not a particular individual should have access to a specific piece of information' (Conway et al, 1972) and security as 'preventing unauthorised access to a file' (Dearnley, 1973). Integrity is defined as 'the safe-guarding by the system of information entrusted to it' (Wilkes, 1972). Thus data base resilience includes the ability to maintain integrity and a particular type of occurrence for which resilience is useful is the breaching of security with a subsequent unauthorised change to the data base. Similar definitions of these terms may be found in Browne (1972).