In recent years, publish-subscribe (pub-sub) systems based on XML document filtering have received much attention. In a typical pubsub system, subscribed users specify their interest in profiles expressed in the XPath language, and each new content is matched against the user profiles so that the content is delivered to only the interested subscribers. As the number of subscribed users and their profiles can grow very large, the scalability of the system is critical to the success of pub-sub services. In this paper, we propose a novel scalable filtering system called FiST (Filtering by Sequencing Twigs) that transforms twig patterns expressed in XPath and XML documents into sequences using Pr¨ufer’s method. As a consequence, instead of matching linear paths of twig patterns individually and merging the matches during post-processing, FiST performs holistic matching of twig patterns with incoming documents. FiST organizes the sequences into a dynamic hash based index for effici...