1. A method for customizing a fixed mapping between a computer program code and a code-model, comprising the steps of: given a fixed mapping between (a) a computer program code expressed in a certain programming language and (b) a code-model expressed in a modeling language, defining customization points in the mapping; and for each customization point, associating a respective mapping key with the customization point, the mapping keys enabling at least one of (i) pieces of the computer program code to be derived from corresponding pieces of the code model, and (ii) pieces of the code-model to be derived from pieces of the computer program code.