An abduction-based method for index relaxation in taxonomy-based sources

The extraction of information from a source containing term-classified objects is plagued with uncertainty. In the present paper we deal with this uncertainty in a qualitative way. We view an information source as an agent, operating according to an open world philosophy. The agent knows some facts, but is aware that there could be other facts, compatible with the known ones, that might hold as well, although they are not captured for lack of knowledge. These facts are, indeed, possibilities. We view possibilities as explanations and resort to abduction in order to define precisely the possibilities that we want our system to be able to handle. We introduce an operation that extends a taxonomy-based source with possibilities, and then study the property of this operation from a mathematical point of view.