Conceptual languages to describe business models - not business process models - become increasingly important. One of the most expressive approaches towards business models is the Resource-Event-Agent (REA) ontology. REA has a substantial back-up in economic and accounting theory, but did lack a dedicated representation language for many years. Recently, we have introduced a domain specific modeling language including a REA meta model and a pertinent graphical notation. In this paper we build upon our previous work, but aim for a representation language that is able to serve as a serialization syntax also for other REA modeling approaches using UML class diagrams or OWL, etc. As a result we come up with REA-XML, an XML schema that allows a precise, tool-independent representation of REA models and that may also serve as an REA model exchange language between different tools.