In some countries, the student's advisor serves as the chair of the doctoral examination or dissertation committees. In some cases, though, the person who serves those roles may be different from the faculty member who has most closely advised the student. For instance, in the Dutch academic system , only full professors ( hoogleraren ) may chair doctoral examinations, so students who have been advised by lower-ranked faculty members will have a full professor as their official advisor (or promotor ) and their actual advisor as co-promotor .  In other countries, such as Spain, the doctoral advisor has the role of a mentor, but is not allowed to form part of the examination committee. This is a body of 5 experts independently selected by the rectorate among 10 candidates proposed by the university's department.