Interview Puzzles :: Discussion

There are n students in a class, each in possession of a different personality attribute. As they are new in the school, so they want to know about each other. To help the students, the teacher decides to conduct an activity. The rule for the activity is that the students will share the personality attributes of each other through a series of bilateral conversations (e.g., via a telephone). Assume that in every conversation both parties exchange all the personality attributes they know at the time. What is the minimum number of conversations they need to guarantee that everyone of them gets all the personality attributes?