Configuration management in a product data management system (PDMS) can provide designers with related components through a product's configuration. The selected components are connected and used for checking for assemblability before they are physically assembled. The assembly rules and constraints are used to help accomplish this task. In this research, we discuss issues in collecting assembly rules and constraints through the product's assembly relations, then integrate them in an assembly model. This model can be used to represent the general design of a product. We also propose a set of modeling procedures to build up the assembly model so that a user can use it to analyze assembly relationships and to check the product's assemblability. Finally, the configuration of a personal computer is used as an example to show how this procedure works and how the assembly rules and constraints for computer assembly are derived.