Current Computer Aided Design (CAD) systems can capture some of the design intent by creating associations between objects. This increases the productivity during product development, and helps maintain the coherence of the product definition when handling engineering changes. CAD systems establish some associations as well as their use at a rather low level of abstraction, e.g. a parallelism constraint. Product Lifecycle Management (PLM) systems, on the other hand, use associations at a higher abstraction level, generally between files. The associations handled by these systems do differ both in terms of abstraction level and formalism of the knowledge they encapsulate. Moreover, limited connections exist between the associations manipulated in both systems, so that handling change propagation in concurrent engineering remains an issue. In this paper, we propose a taxonomy and a model of the different types of associations required to support the set of tasks in the area of product development. The terms on which the taxonomy relies are: association, relation, link, and constraint. The proposed model, named RLC, uses the concepts of aggregation and decomposition to relate Relations, Links, and Constraints.