Logical Handling of Inconsistent and Default Information

The subjects of this chapter are two important and related kinds of uncertainty in information systems: inconsistent information and default (defeasible) information. In many information system applications, there is a need to represent and reason with inconsistent data. For example, in a tax collection agency, database records on individual taxpayers should be allowed to have inconsistent information, as such information could be used to direct enquiries by tax inspectors. Default information , such as rules that are usually true but are allowed to have exceptions, tends to reduce the size of databases significantly, yet without significant loss of utility for many applications. For example, a market research agency could use default information in its consumer profiles: for its kind of business such a level of accuracy could be deemed sufficient.