Searching and Tagging: Two Sides of the Same Coin?

This paper presents the duality hypothesis of search and tagging, two important behaviors of web users. The hy- pothesis states that if a user views a document D in the search results for query Q, the user would tend to assign document D a tag identical to or similar to Q; similarly, if a user tags a document D with a tag T, the user would tend to view document D if it is in the search results obtained using T as a query. We formalize this hypothesis with a unifled probabilistic model for search and tagging, and show that empirical results of several tasks on search log and tag data sets, including ad hoc search, query suggestion, and query trend analysis, all support this duality hypothesis. Since the availability of search log is limited due to the privacy concern, our study opens up a highly promising direction of using tag data to approximate or supplement search log data for studying user behavior and improving search engine accuracy.