Many Web information services utilize techniques of information extraction (IE) to collect important facts from the Web. To create more advanced services, one possible method is to discover thematic information from the collected facts through text classification. However, most conventional text classification techniques rely on manual-labelled corpora and are thus ill-suited to cooperate with Web information services with open domains. In this work, we present a system named LiveClassifier that can automatically train classifiers through Web corpora based on user-defined topic hierarchies. Due to its flexibility and convenience, LiveClassifier can be easily adapted for various purposes. New Web information services can be created to fully exploit it; human users can use it to create classifiers for their personal applications. The effectiveness of classifiers created by LiveClassifier is well supported by empirical evidence. Categories and Subject Descriptors H.3 [Information Storage...