Product data interchange occurs for very different purposes. The situation that puts the severest requirements on the interchange process is data sharing for simultaneous product design, when multiple tools are working on a common data representation. This application deserves study as it is a crucial factor to enable concurrent engineering and to make the design process less sequential. Transaction management for data sharing is hampered by three factors: size and complexity of the engineering data, the large multitude of design functions or data operations, and the incompatibility of the design tools involved especially when they originate from different commercial vendors. Traditional data exchange techniques using neutral data formats cannot cope with the data sharing problem. Advanced conversion methods are needed to translate the tool-specific data representations into each other without losing the semantics. In addition, a consistency checker is required during simultaneous use of the common data to prevent that an operation performed by one of the tools makes the data invalid or meaningless to the other tools involved. This consistency checker can be made on basis of an analysis of the design tools, their data representation forms and their operations. Such analysis has been made for two commercial CAD systems which are used jointly for a design task. The analysis shows that it is feasible to maintain consistency of the data while performing tasks simultaneously, thus shortening the design time.