1. A method for extending a model-to-model transformation, the method comprising the steps of: obtaining an instance of a model-to-model transformation in memory of a computer; selecting all extensions that specify the model-to-model transformation and instantiating the selected extensions; merging in the memory of the computer the extensions to the model-to-model transformation with the instance of the model-to-model transformation to produce an instance of an extended model-to-model transformation, the extensions each identifying portions of the model-to-model transformation to be extended, and the extensions each specifying different transform elements to be inserted into the identified portions of the model-to-model transformation.