Specification and efficient processing of similarity queries on multimedia databases have recently attracted several research efforts, even if most of them have considered specific aspects, such as indexing, of this new exciting scenario. In this paper we try to remedy this by presenting an integrated algebraic framework which allows many relevant aspects of similarity query processing to be dealt with. As a starting point, we assume the more geenral case where "imprecision" is already present at the data level, typically because of the ambiguous nature of multimedia objects' content. We then define a generic similarity algebra, SAME~W, where semantics of operators is deliberately left unspecified in order to better adapt to specific scenarios. A basic feature of SAME~W is that it allows user preferences, expressedin the form of weights, to be specified so as to alter the default behavior of most operators. Finally, we discuss some issues related to "approximation" and to "user evaluation" of query results.
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