Qualitative Methods for Reasoning Under Uncertainty

In this book Simon Parsons describes qualitative methods for reasoning under
uncertainty, "uncertainty" being a catch-all term for various types of imperfect information. The
advantage of qualitative methods is that they do not require precise numerical information. Instead,
they work with abstractions such as interval values and information about how values change. The
author does not invent completely new methods for reasoning under uncertainty but provides the means
to create qualitative versions of existing methods. To illustrate this, he develops qualitative
versions of probability theory, possibility theory, and the Dempster-Shafer theory of
evidence.

According to Parsons, these theories are best considered complementary
rather than exclusive. Thus the book supports the contention that rather than search for the one
best method to handle all imperfect information, one should use whichever method best fits the
problem. This approach leads naturally to the use of several different methods in the solution of a
single problem and to the complexity of integrating the results problem to which qualitative methods
provide a solution.