A method and system customize and thus extend a fixed mapping between a computer program code language and a code-model notation. Given a fixed mapping, the invention method and system define customization points in the mapping based on known/predefined relatively over rigid points. For each customization point, there is a respective mapping key that enables a piece of the computer program code to be derived from a corresponding piece of the code-model, and vice versa. The code-model reflects the customizable perspective, and contents of the code-model can be tailored to elide implementation details.