The choice of solution, which a systems architect is confronted with within the framework of a product structure definition, can very quickly prove to be a thorny problem owing to the possible combinatorial system. In this paper, we will offer an alternative resting on the utilization of constraint-based programming techniques for representing and managing such complexity. More precisely, we will dwell on the presentation of a constraint-based approach to the composition relation management of a product class in design. After setting forth all the potential of the constraint-based approach, we will formally explain, in more detail, the six types of relations that seem to be essential to building a class of products. The approach is based on a three-level architectural model. The first level concerns the product model as such, the second supplies a formal representation of this model, whereas the third consists of rendering an arithmetic constraint-based approach to the intermediate model. We will use the discrete constraint satisfaction problems for operating and solving the latter. Our overall approach, from product modeling to resolution, is intended to be a generic one and the case in point will be the design of a functional pivot link between a connecting rod and a piston. The architect can subsequently make his own choices and the tool will automate their propagation by means of the constraint network modeling the problem. A dimensioning architectural model is, thus, obtained in compliance with the original list of requirements.