Queries With Ordering Based On Similarity

The fuzzy sets allow represent vague concepts where membership of an object can be gradual. It has been proposed the use of this theory in databases. As result, fuzzy relational model and some extensions to the SQL language have emerged. In particular, domains with features fuzzy can supply the attributes of a relation. The implications of these attributes kind over query operators based on the ordering of data have not been sufficiently explored. This paper tackles to the definition of attributes in domains with a similarity fuzzy relation, which is an extension of equivalence relations in fuzzy set theory. We propose a new definition for similarity fuzzy relations that are more appropriate to the problem of databases. We extend SQL to define and manipulate these domains. We extend the ORDER BY clause for queries with orderings based on similarity relations. These extensions increase the expressivity of the database language, with respect to previous proposals.