the conference is identified by the year (unique) and described by city, location, chairman, an organizing committee, a set of participants, and a set of papers (articles). It is required to keep track of the total number of participants and papers for each conference occurrence.
participant is identified by a number (unique), and described by a name, category (distinguished lecturer, chairman, member of an organizing committee, author... etc.) and E-mail address. A participant in any conference occurrence may pay certain fees which is determined according to his/her category. It is required to keep track of the total fees for each particular conference occurrence