1. A computer-implemented method for compressing a three-dimensional modeled object, wherein the method comprises: providing an input boundary representation of the modeled object, the input boundary representation comprising geometrical data, the geometrical data including functions each corresponding to a respective geometrical entity, each function having a domain and a range, the functions including: a reference function corresponding to a reference geometrical entity, the reference geometrical entity being obtained by applying the reference function; and another function corresponding to another geometrical entity, the other geometrical entity being obtainable by applying the other function; producing first data, that describe a mapping from the range of the reference function to the range of the other function, and second data, that describe a mapping from the domain of the other function to the domain of the reference function which, when composed with the reference function and the mapping from the range of the reference function to the range of the other function results in the other geometrical entity; and determining an output boundary representation, the output boundary representation comprising the geometrical data with the other function replaced by the first data, the second data and a pointer to the reference function, the output boundary representation comprising a compressed modeled object usable by a CAD (Computer-aided Design) system.