This paper describes a description approach for modeling product-process information in the contexts of assembly oriented design and product lifecycle management (PLM). The growing evolution of models, methodologies, systems and tools over the entire product lifecycle has highlighted limits and difficulties – such as the awareness and understanding in engineering – that did not exist before. An emergent challenge remains in increasing awareness and understanding of actors in the management of product information and knowledge. This requires effort in new inspired approaches in the qualitative representation and reasoning of the product and processes, in ontological applications, knowledge-based approaches, models, etc. The main objective is to make assembly information consistent, accessible and exploitable by data management systems and computer-aided X tools by introducing a logical foundation. In this context, product-process relationships are considered and described in the part-whole theory supported by mereology and its extension, mereotopology, then implemented in an ontology.