The Simple Extensible Data Format (SXDF) defined in this document aims to combine the nice properties of XML (of providing a universal, text-based data format which allows adding additional data fields without breaking existing application programs) with a simple syntax which can be parsed efficiently by computer programs. This data format is intended for over-the-wire use in webservice protocols, where there is generally no interest in being able to directly modify the representation of the data with a standard text editor.