In order to publish a nested XML document from flat relational data, multiple SQL queries are often needed. The efficiency of publishing relies on how fast these queries can be evaluated and their results shipped to the client. We illustrate novel optimization techniques that enable computation sharing between queries that construct sibling elements in the XML tree. Such queries typically share large common join expressions that can be exploited through appropriate rewritings. These rewritings are fundamental to XML publishing and provide considerable performance benefits without having to modify the relational engine.