Accommodating subjective vagueness through a fuzzy extension to the relational data model

Expression and processing of vagueness, which has many real world applications, are not handled effectively in the conventional relational data model. In this paper we investigate a fuzzy extension to the relational data model and propose three fuzzy relational query languages. Two of them are the Level-1 Fuzzy Relational Algebra and Level-1 Fuzzy Relational Calculus. They are fundamental query languages and serve as a theoretical framework for the fuzzy relational database. Finally, the Fuzzy Selectiue Relational Algebra is presented to express fuzzy constants and fuzzy comparators, which are more effective to represent vagueness in user queries. We show that the three proposed query languages have the same expressive powers. We also present various aspects of the proposed model and its functional advantages over the conventional relational data model.