Advancement to Candidacy, PhD in Computer Science
The only goal of the candidacy/qualifying/preliminary exam is to convince the committee that you deserve to pass the candidacy/qualifying/preliminary exam.  The passing criteria differ, sometimes radically, from one university to the next, from department to the next, from one research area to the next, and even from one committee member to the next.  It's the academic equivalent of Calvinball, only you don't get to make up the rules.  Do not question the mask.

The only way to determine how to prepare for the candidacy/qualifying/preliminary exam is to ask your committee members directly.  Individually.  In person.  I strongly recommend scheduling a one-on-one meeting with each committee member at least a month in advance of the actual exam.

Same goes for the thesis defense.