RL-instances: An alternative to conjunctive fuzzy sets of tuples for flexible querying in relational databases

In this paper we introduce RL-instances as a way to represent and manipulate gradual conjunctive collections of tuples. Our proposal, based on the theory of Representation by Levels, overcomes the limitations of fuzzy instances in keeping all the properties of conventional Relational Algebra operations. We provide a proof of concept implementation in a conventional relational database management system, where flexible queries can be performed on crisp tables using the same patterns that are used in conventional querying.