Abstract Social bookmark service is a tool to classify information on the web with user s own criteria. Organizing website with social bookmark service is fundamentally conducted for individual s benefit. However, stored list of websites and annotation, especially tags, keyword to indicate classification, help all users searching appropriate information effectively. There are three features of activity at social bookmark services and generated data. First, social bookmark services make users cooperate for making more use of information unintended. Second, usage of vocabulary for tags is uniformed without external control. In other words, bottom-up metadata description has prospects of building Folksonomy. Third, tags perform to be medium for communication, and affect users purchase behavior. Social bookmark service is ascribed to platform of unintended cooperation and generates information commons to help users searching information effectively. 6
Unintended cooperation: information commons made of meta-data with bottom-up production 7
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