The problem of processing XML streaming data fits a large class of new applications and has been a hot spot recently. The XML streams on the World Wide Web are usually autonomous, distributed and heterogeneity. All existing methods, however, do not support processing a collection of XML streams from heterogeneity data sources. In this paper, we address the heterogeneity issues in the context of XML stream processing. We use the global ontology based on RDF as a mediator, translate a global query written by RDQL into a set of target queries for various sources, and construct corresponding query state machines (extended finite automation) for querying XML streams.