An Approach to Fuzzy Database Querying, Analysis and Realisation

Although the Structured Query Language (SQL) is a very powerful tool, it is unable to satisfy needs for data selection based on linguistic expressions and degrees of truth. The goal of the research whose results are presented in the paper is to capture these expressions and make them suitable for queries. For this purpose the fuzzy generalised logical condition for the WHERE part of SQL was developed. In this way, queries based on linguistic expressions are supported and are accessing relational databases in the same way as with the SQL. Fuzzy query is not only a querying tool; it improves the meaning of a query and extracts additional valuable information. Statistical data about districts of the Slovak Republic are used in the case study. Fuzzy approach has some limitations that would appear in a querying process. These limitations and ideas how to solve them are outlined in this paper.