Mohamed Shehab Elisa Bertino Arif Ghafoor Watermarking Relational Databases Using Optimization-Based Techniques. 116-129 2008 20 IEEE Trans. Knowl. Data Eng. 1 http://doi.ieeecomputersociety.org/10.1109/TKDE.2007.190668 db/journals/tkde/tkde20.html#ShehabBG08