Business-to-consumer and business-to-business applications based on the Extensible Markup Language (XML) tend to lack a rigorous description of product data, the information generated about a product during its design, manufacture, use, maintenance, and disposal. ISO 10303, also informally known as the Standard for the Exchange of Product model data (STEP), defines a robust and time-tested methodology for describing product data throughout the lifecycle of the product. I discuss some of the issues that arise in designing an XML exchange mechanism for product data and compare different XML implementation methods currently being developed for STEP.