In this paper, we outline a possible formalization of the semantics of the XML-based ODX language. ODX is a substantial part of the emerging automotive ASAM MCD standard, which describes a middleware layer between offboard diagnosis applications and onboard diagnosis services of electronic control units (ECUs) of cars. The contribution of our work is threefold: Firstly, a consequent application of our results can contribute to a well-structured development process in the automotive diagnosis domain. We are currently showing this in practice as part of our ongoing cooperation with the diagnosis department of AUDI AG. Secondly, our proposition is the first step towards guaranteed standard-conformity of implementations of the MCD run-time system, also specified by the standard and strongly depending on ODX and its semantics. Last but not least, the paper can serve as an encouraging example of the application of formal methods in practice.