The object-oriented paradigm is very used in CAD systems. It permits users to create objects and to interrogate their attributes to use them in other processes. While some CAD or drawing systems support end-user programming in order to abstract building functions, none of them permit creating classes where several functions (constructor and selectors) share the same data. A data model that permits to abstract a class from one of its instances built by the end-user is described in this paper. The proposed technique permits the user not only to describe interactively the class constructor, but also to build the class selectors without any programming knowledge. The created class can be used directly thanks to a specific interpretation mechanism, or the corresponding code can be generated and compiled to have persistent classes. This technique has been used in a CAD system that permitting end-user specialization.