The invention provides the ability to interactively select and configure a product among a set of related products based on availability and compatibility of features and options. It does not impose an order in the selection of products, features or options; only valid selections can be made at any time. To create an electronic representation of the product information to achieve the above goal, the invention provides a framework for defining a systems by defining the components of the system using elements contained in a parts catalog and defining relationships between the components of a system. A configuration system validates a configuration using the system definition, the current state of the configuration and user input.