Using Fuzzy Sets in Flexible Querying: Why and How?

The last few years have witnessed a tremendous increase in the use of computers in more and more domains, the need for managing new kinds of data and for providing new capabilities for storage, access and display of information. In this respect, one may imagine introducing what is often dubbed “uncertainty” ’into databases. This term may refer to two main streams of problems. On the one hand, one wants to store and manipulate incomplete data (i.e., the available information about attribute values may be tainted with imprecision and/or uncertainty for some items) . In that case, the retrieval process will also return results involving some uncertainty (if we are uncertain about the precise value of John’s age, we cannot always be sure that John does (or does not) satisfy a given requirement in the context of a query selecting people on basis of their age). On the other hand, the term “uncertainty” is sometimes (and somewhat misleadingly) used for referring to flexible queries, since one may then consider that there is some ambiguity pertaining to their meaning. In fact, flexible queries are useful for describing preferences and thus for getting an ordered set of answers accordingly.