Fuzzy Queries Based on Linguistic Variables in Relational Databases

The concept of weight is introduced in fuzzy queries based on theory of fuzzy set,which shows the relative importance that users pay to different attributes in query clauses.The records that satisfy queries are output according to the decrease of matching degrees,so users can select what they want more conveniently.Weights and matching degrees are linguistic variables,whose values are linguistic terms,and the queries become more flexible.The alpha-cut of fuzzy set is used to translate the linguistic fuzzy querying conditions into crisp SQL clauses.It is possible to make use of the mechanism of RDBMS to filter the records,which avoids scanning the whole table and assures the efficiency.