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The watermarking technique can be used to protect the copyright of relational databases by hiding the ownership information into the relational databases. Difference expansion (DE) technique is one of the common reversible watermarking techniques for numerical relational databases. However, most previous schemes based on DE suffer the problem of low embedding capacity when the difference values between different attributes are relatively large. In this paper, we propose a novel reversible watermarking scheme to solve the above problem. In the scheme, a mapping difference expansion (MDE) method is proposed to convert the differences between attributes to small mapping differences. Based on the MDE, an attribute and tuple selection algorithm is designed to select the suitable data for watermarking, which can increase embedding capacity and reduce distortion. In addition, the majority voting technique is utilized to enhance the robustness of watermarking with the high embedding capacity. The experimental results have shown that the proposed scheme can provide higher embedding capacity, lower distortion and stronger robustness than other schemes.
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