That is, each person, organization or group belongs to specific categories, and a category belongs to higher-level categories. In the competition, both users and items (person, organizations and groups) are represented as anonymous numbers that are made meaningless, so that no identifying information is revealed. The data consists of 10 million users and 50,000 items, with over 300 million recommendation records and about three million social-networking "following" actions. Items are linked together within a defined hierarchy, and the privacy-protected user information is very rich as well. The data has timestamps on user activities.
