A similarity based relational algebra for Web and multimedia data

Web and multimedia data are becoming very important. A fundamental characteristic of these data is imprecision. Query languages for Web and multimedia data must express imprecision in features matching, similarity queries and user preferences. In addition specific operators need to be introduced to organize the answers in a user friendly style. The aim of this work is to provide a formal framework in which to formulate very powerful queries and presentations of the answers. To this end, a fuzzy based algebra is introduced. The fuzzy algebra extends the classical relational algebra over fuzzy relations with new operators. Both algebras allow user preferences in the form of weights to be attached to predicates and operators. The effect of this weights is to alter the classic behavior of query expressions to better suite user requirements. In addition, optimization issues are presented in the form of algorithms for the efficient evaluation of similarity based queries, containing new algebraic operators. (C) 2002 Elsevier Science Ltd. All rights reserved.