Abstract: A Fuzzy Query Language (FQL) for relational databases is proposed FQL, developed as an extension of relational domain calculus, has sufficient capabilities to express all five types of fuzzy statements distinguished and represented in a meaning representation language PRUF by Zadeh. The main idea for developing FQL lies in a method that hannoniously integrates relational domain calculus and PRUF, together with a natural determination method of matching degrees of domain values in relational databases against FQL queries. Effects of FQL are twofold. One is practical. We expect that FQL will add a human-oriented interface to currently widespread relational databases all over the world that have already stored a vast amount of useful information. In addition, fuzzy expert systems currently under development can be designed to support FQL so that they can make usc of fact data stored in some relational database in their processing. The other but principal effect is theoretical. FQL provides a theoretical framework that can play a kernel role in integrating many previous-and-future fuzzy extensions of relational database query languages systematically into a unified fuzzy query language.
Takahashi REF proposed the Fuzzy Query Language that is an improvement of the relational domain calculus.