PhD students are required, during their PhD period, to attend and pass 6 exams of courses offered by our PhD (they are listed below) or by other PhDs. 
They can even consider courses offered by the Master Degree in CS, or International PhD Schools, which can be useful for deepen into some specialization areas or covering key CS topics that are missing in their background. 
In any case, the list of courses chosen by the PhD student has to be approved (in advance) by the PhD Committee.