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NIST Express Working Form Programmer



Steve Clark, Donald E. Libes


The Product Data Exchange using STEP (PDES) is an emerging standard for the exchange of product information among various manufacturing applications. PDES includes an information model written in the Express language; other PDES-related information models are also written in Express. The National PDES Testbed at NIST has developed software to manipulate and translate Express models. This software consists of an in-memory working form and an associated Express language parser, Fed-X. The internal operation of the Fed-X parser is described. The implementation of the data abstractions which make up the Express Working Form is discussed, and specifications are given for the Working Form access functions. The creation of Express language translators using Fed-X is discussed.

This document has been revised to reflect modifications in the implementation of Fed-X software to support changes in the Express language.

NIST Interagency/Internal Report (NISTIR) - 4814
Report Number


Express language, information model, PDES, STEP


Clark, S. and Libes, D. (1992), NIST Express Working Form Programmer, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed June 18, 2024)


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Created May 31, 1992, Updated October 12, 2021