Over the last decades, concurrent engineering and design for X approaches have introduced knowledge-based decision supports, analysis methods and feature-based modelling techniques to deliver designed solutions ready for specific lifecycle purposes. However, to cover the emerging knowledge synthesis issue in engineering design, the underlying 3D representations need to be better understood and chained. This paper aims at developing original multi-representation and multi-scale CAD models to integrate properly knowledge in their most suitable form. Reconciliation mechanisms can be set up to validate semantic continuity of the geometric models and to justify the knowledge structuring the design solutions space.