A versioning schema enforced by the application development environment enables the runtime environment of a terminal device to evaluate a software update to identify potential compatibility issues and control installation of the update. The versioning schema includes a respective field for each one of a plurality of aspects of the application and defines an initial value of each field when an initial application load is released. For each successive software update affecting the application, the method involves identifying each aspect of the application affected by the software update and incrementing a value of the respective field of each identified aspect. The version number can be in the form D.M.F where D, M and F are incremented in response to changes in the application relating to data components, message components and features.