PDE/STEP规范允许工程应用程序交换有关产品的信息。与以前的工程信息规范不同，这些规范包含一种称为EXPRESS的数据定义语言，可用于描述任何类型的工程数据。希望使用PDE/STEP交换数据的应用程序可以通过编写特定软件来处理一种产品的PDE/STEP模型，或者编写通用软件来处理任何类型产品的任何PDE/STEP模型的明确描述。本文描述了面向对象技术如何实现后一种情况。

THE PDES/STEP SPECIFICATIONS ALLOW ENGINEERING APPLICATIONS TO EXCHANGE INFORMATION ABOUT PRODUCTS. UNLIKE PREVIOUS SPECIFICATIONS FOR ENGINEERING INFORMATION, THESE SPECIFICATIONS CONTAIN A DATA DEFINITION LANGUAGE CALLED EXPRESS THAT CAN BE USED TO DESCRIBE ANY TYPE OF ENGINEERING DATA. APPLICATIONS THAT WANT TO EXCHANGE DATA USING PDES/STEP CAN DO SO BY WRITING SPECIFIC SOFTWARE TO PROCESS ONE PDES/STEP MODEL FOR ONE TYPE OF PRODUCT, OR THEY CAN WRITE GENERIC SOFTWARE TO PROCESS THE EXPRESS DESCRIPTION OF ANY PDES/STEP MODEL FOR ANY TYPE OF PRODUCT. THIS PAPER DESCRIBES HOW OBJECT-ORIENTED TECHNOLOGY CAN IMPLEMENT THE LATTER CASE.