The goal of this article is to show that, in the context of XML data processing, information conveyed by schema or XML types is a powerful component to deploy optimization methods. We focus on the one hand on recent work developed for optimizing query and update evaluation for main-memory engines and on the other hand on techniques for checking XML query-update independence. These methods are all based on static type analysis. The aim of the article is to show how types rank before constraints for XML data processing and the presentation of each method is kept informal.