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We formally investigate the problem of retrieving the best results complying with multiple preferences expressed in a logic-based language when data are stored in relational tables with taxonomic domains. We introduce two operators that rewrite preferences for enforcing transitivity, which guarantees soundness of the result, and specificity, which solves conflicts among preferences. We show that these two properties cannot be achieved together and identify the only two possibilities to ensure transitivity and minimize conflicts. Our approach proves effective when tested over both synthetic and real-world datasets.