https://uomosul.edu.iq/computerscience/%d8%a3%d8%b7%d8%b1%d9%88%d8%ad%d8%a9-%d8%af%d9%83%d8%aa%d9%88%d8%b1%d8%a7%d9%87-%d8%a8%d8%b9%d9%86%d9%88%d8%a7%d9%86-protection-of-relational-databases-by-means-of-watermarking/