When does a PhD end? I know this is a very general question on this forum, but let us consider a CS-engineering group. What is the usual and primary consideration for letting the student finish officially?
Is it the number of years spent, when the professor feels nothing more useful will come out of working on the problem (or of the student!)?
Is it the logical conclusion of the problem and the thesis? A student works to complete a problem in 3 years and publishes a couple of journal papers, and finds there is no more to the problem. Will he be allowed to finish or forced to work on some tangential problem simply to prolong his PhD?