A computer system and implemented method for defining an input product to be manufactured into an output product, comprises steps of: (a) receiving an output product having attributes and comprising at least one sub-product, said sub-product having attributes; (b) associating to said output product a manufacturing operation identified among a plurality of manufacturing operations; (c) defining attributes of said input product, said input product attributes deriving from modification of attributes of the at least one sub-product according to the associated manufacturing operation. The computer implemented method of the invention thus derives input products from the output product to be manufactured with a process oriented approach. Design modifications on output product can be directly and automatically taken into account in input products.