In methodical product development, numerous data are used and linked with each other, especially variant-related data. This paper presents a model-based solution for avoiding inconsistencies in the development of product families with many variants and extends it to modular lightweight design. In addition, the inconsistencies in methodical product development were classified and solution approaches were shown. Thus, inconsistencies can be avoided with the presented elaborated data model for an integrated product and process model based on the presented procedure.