1. Computer-implemented method for the editing of three-dimensional graphic models, including: preparing a three-dimensional feature-based graphic model using a computer, said three-dimensional feature-based graphic model including a plurality of structural elements, each associated with one or more of the other structural elements according to a data structure, said data structure including sufficient data for a complete description of said three-dimensional model, said data structure including geometry and topology information, features parameters, constraints and relationships; generating a first set of additional data, said first set of additional data representing supplementary geometrical and/or positional and/or semantic data and relationships between said structural elements, said additional data not representing features and related parameters, constraints and relationships available in conventional feature-based models; receiving at least one modifying signal, representing a modification to be made on at least one predetermined structural element exploiting said first set of additional data; modifying, in accordance with said modifying signal, the predetermined structural element and the structural elements associated therewith according to said data structure and said first set of additional data, thereby updating said data structure and said first set of additional data, obtaining a corresponding modified three-dimensional graphic model, displaying said corresponding modified three-dimensional graphic model on a computer screen connected with said computer.