15. A computer storage medium having computer-executable instructions, which when executed perform actions, comprising: obtaining first configuration data for an application that is operable to execute in a first environment; obtaining transformation data that indicates modifications to make to the first configuration data to create second configuration data suitable for when the application is executing in a second environment, the transformation data encoded in a declarative language; transforming the first configuration data according to the modifications indicated in the transformation data to create the second configuration data; and wherein the first configuration data and the transformation data have an identical schema that expresses constraints on structure and content of the first configuration data and the transformation data, the constraints additional to constraints imposed by one or more languages in which the first configuration data and the transformation data are represented.
20. The computer storage medium of claim 15 , wherein a first declarative statement of the transformation data indicates a file and an element of the first configuration data, the file including additional declarative statements that indicate one or more modifications to make to the element of the first configuration data, transforming the first configuration data including applying the one or more modification to the element of the first configuration data.