Differential index update in cooperative search engine

Cooperative search engine (CSE) is a distributed search engine, which can update index in very short time for the purpose of fresh information retrieval. Although CSE´s retrieval response time is longer than general centralized search engines, we develop some techniques to accelerate CSE´s retrieval response time. As a routine work, CSE finds new documents and new words, and updates the index. In this daily update process, removed documents and words were not considered due to update processing speed. So we develop a new daily update process, differential update. Differential update considers added, modified and removed documents and words. We describe the behavior and evaluation of the differential update.