A system of software, named CODER, has been written which can analyze the solid model of a part and generate a group technology part code through the identification of form features. The CODER algorithm is bottom-up in nature, first searching for small form-features and then constructing macro-features from the small elements. The program has been implemented using logic programming techniques and consists of facts, describing the part, which must be searched to satisfy rules defining the form-features. The rules and facts are written in Prolog. The facts are generated automatically in Prolog from the ROMULUS2 solid modeler. Rules can define form-features specific to a particular coding scheme and, therefore, form a code-specific knowledge base. The significance of this research is seen when applied to the many designs which have been generated on wire frame CAD systems in the past and, which, if converted to solid models, could be automatically coded for variant process planning, design retrieval and other applications germane to part coding. The algorithm is written in a combination of Prolog, Lisp and S.I™3.