About yes/no queries against possibilistic databases

Abstract

This article is concerned with the handling of imprecise information in databases. The need for dealing with imprecise data is more and more acknowledged in order to cope with real data, even if commercial systems are most of the time unable to manage them. Here, the possibilistic setting is taken into consideration because it is less demanding than the probabilistic one. Then, any imprecise piece of information is modeled as a possibility distribution intended for constraining the more or less acceptable values. Such a possibilistic database has a natural interpretation in terms of a set of regular databases, which provides the basic gateway to interpret queries. However, if this approach is sound, it is not realistic, and it is necessary to consider restricted queries for which a calculus grounded on the possibilistic database, that is, where the operators work directly on possibilistic relations, is feasible. Extended yes/no queries are dealt with here, where their general form is: "to what extent is it possible and certain that tuple t~given! belongs to the answer to Q," where Q is an algebraic relational query. A strategy for processing such queries efficiently is proposed under some assumptions as to the operators appearing in Q.

Modeling and Querying Uncertain Relational Databases: A Survey of Approaches Based on the Possible Worlds Semantics

“…, A n . It has been proven in (Bosc and Pivert, 2007) 25 that such a transformation is also valid in an imprecise database framework inasmuch as the model used is a strong representation system (which is the case here). It is then possible to compute the final possibility and necessity degrees by means of a straightforward adaptation of the algorithm presented above, cf.…”

“…Bosc et al 24,25 use the framework of possibilistic databases and deal with so-called generalized yes-no queries -generalized because their answer is not yes or no but a pair of degrees -whose general format is: "to what extent is it possible and certain that the answer to Q fulfills condition C?" where Q is a (constrained) relational algebraic query which may include only the operators for which the model is an SRS, i.e.…”

“…It is then possible to compute the final possibility and necessity degrees by means of a straightforward adaptation of the algorithm presented above, cf. (Bosc and Pivert, 2007) 25 for more detail.…”

“…Indeed, one does not need to represent the result of Q but only the union of its results in the different worlds of the imprecise database considered. See (Bosc and Pivert, 2007) 26 for more details.…”