Yahoo! Answers, OKWave and Baidu Zhidao, have become popular web services. In these services, a user posts a question and other users answer it. The questioner chooses one of the answers as the best answer. These services have many threads consisting of one question and a number of answers, and the number of threads grows day by day. The threads are stored and anyone can read them. When a user has a question, if there is a similar question in the service, he or she can refer to the answers to the similar question. Herefrom, these services are useful for not only the questioner but also other users having a similar question. Community-based Question Answering services, such as Yahoo! Answers, OKWave, and Baidu Zhidao, have become popular web services. As the name suggests, on such services, a user posts a question, other users answer it, and the original questioner selects the best answer. Typically, such services have an increasing number of threads comprising a single question and multiple answers. The threads are stored and are publicly available. If a user posts a question similar to one stored in the system, they can refer to the answers to the stored question. 出⼒⽂書 𝑑’ • ⼊⼒⽂書 𝑑 が与えられたとき,⾃動リビジョンシステム 𝒇 は元の意味を保持しつつ⽂書 単位で品質を向上させるためのリビジョン 𝑹 を⾏い出⼒⽂書 𝑑’ を返すタスク (𝑓: 𝑑 ⟼ 𝑑’) • リビジョン 𝑹 は編集 𝒆 の集合からなる (𝒆 ∈ 𝑹) システム 𝒇 編集 𝒆 編集 𝒆 リビジョン 𝑹