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 consider courses offered by the Master Degree in CS (at most one), or International PhD Schools (at most two), 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.