The concept of a bulletin board system (BBS) equipped with information visualization techniques is proposed for supporting online data analysis. Although group discussion is known to be effective for analyzing data from various viewpoints, the number of participants is limited by time and space constraints. To solve that problem, this paper proposes to augment a BBS, a popular web based tool. In order for discussion participants to share data online, the system provides them with a visual representation of target data, which elicits comments from participants as well as compares these comments. In order to illustrate the concept's potential, a BBS equipped with KeyGraph is also developed for supporting online chance discovery. It has functions for making visual annotations on the KeyGraph as well as a function for retrieving similar scenarios. The experimental results show the effectiveness of the BBS in terms of the usefulness of scenario generation support functions as well as that of scenario retrieval engines.