“…Thus, two streams of research in data modeling have emerged, namely, fuzzy extensions to the ER models [24,26,31], which lead to fuzzy ER/EER models allowing Table 2 The closeness relation c Performance imprecise and uncertain concepts to be represented and manipulated at a conceptual level, and fuzzy extensions to the RDB model [1,4,8,14,19,21,23], which allow imprecise attribute values and linguistic constraints to be combined into the classical context. Since the early 1980s, the research on fuzzy relational databases has centered on the problems of how to represent fuzziness in database models, and how to formulate queries in linguistic terms.…”