STEP Part 21

STEP Part 21
Name	STEP Part 21
Other names	ISO 10303-21
Status	Active
Domain	Industrial automation, Product data
First published	1994
Governing body	ISO
Related standards	ISO 10303 series, AP203, AP214, AP242

STEP Part 21 STEP Part 21 is the ISO 10303-21 specification that defines a plain text file protocol for exchanging product data between CAD, CAM, CAE, PLM and PDM systems. It provides a structured container for EXPRESS schemas, instances, and metadata to enable interoperability among vendors such as Dassault Systèmes, Siemens, PTC (company), Autodesk, Bentley Systems and integrators like IBM, Accenture, Capgemini and General Electric.

Overview

The specification establishes a common interchange format used by aerospace suppliers such as Boeing, Airbus, Lockheed Martin, Northrop Grumman and automotive manufacturers including Toyota, Volkswagen Group, Ford Motor Company, General Motors and BMW. It underpins exchanges in programs like IGES-adjacent workflows, complements standards from IEC, IEEE and SAE International, and interfaces with data models used by SAP SE, Oracle Corporation and Siemens PLM Software. Organizations including ISO technical committees, ISO/TC 184, STEP Tools, Inc., NIST and The Open Group reference Part 21 in conformance testing, supply chain integration, and archival preservation projects at institutions like the Smithsonian Institution, National Archives and Records Administration and research centers such as CERN.

Scope and Structure

Part 21 specifies the logical blocks of an exchange file: header section, data section, and optional binary segment markers used in compound files for geometry, metadata and application-specific content. It is used to encapsulate EXPRESS schemas created in environments from providers like Dassault Systèmes CATIA, Siemens NX, PTC Creo, Autodesk Inventor and neutral model producers such as Parasolid and Open CASCADE. The standard is referenced by application protocols like ISO 10303-203, ISO 10303-214, ISO 10303-242 and projects run by consortia including POSC Caesar Association, BuildingSMART International and suppliers to NASA and ESA.

File Format and Syntax

A Part 21 file is an ASCII-based container with a HEADER section containing file schema, creation author and organization attributes, followed by a DATA section of entity instances expressed as numbered records. Implementations parse tokens such as DATA, ENDSEC, and END-ISO-10303-21 along with record tags generated by CAD kernels from Parasolid, ACIS, OpenCASCADE and geometry systems by HOOPS. The syntax accommodates EXPRESS instances defined by languages and tools like EXPRESS-G, Gellish, STEP-NC and EXPRESS compilers maintained by vendors such as EuroSTEP and research groups at Fraunhofer Society.

Implementation and Tools

Toolchains for producing and consuming Part 21 include native exporters in CATIA, NX, Creo, Inventor and neutral translators from TranscenData, Datakit, Lattice Technology and open-source libraries like Open CASCADE Technology and IfcOpenShell. Validation and visualization tools used in industry include products from Siemens PLM, MSC Software, Ansys, AVEVA and inspection suites provided by Hexagon AB. Corporate implementers integrate Part 21 flows with enterprise systems from SAP, Oracle, Microsoft and cloud providers such as Amazon Web Services, Microsoft Azure and Google Cloud Platform during digital thread and digital twin initiatives led by Siemens Energy, GE Aviation and Rolls-Royce.

Conformance and Validation

Conformance to Part 21 requires correct schema declaration, well-formed entity instances, adherence to character encoding and proper use of header attributes. Certification and testing are pursued by labs and consortia like NIST, ISO/TC 184/SC 4, The Open Group and commercial test houses used by Boeing and Airbus suppliers. Tools for syntactic and semantic checking include EXPRESS validators, STEP translators from PDMWorks, quality assessment systems from Verisurf and unit test harnesses developed by research groups at MIT, Caltech, ETH Zurich and University of Michigan.

History and Revisions

Developed as part of the ISO 10303 initiative in the early 1990s, Part 21 evolved alongside AP catalogs such as AP203 and AP214 to support evolving CAD kernels and neutral data needs of Lockheed Martin programs and automotive consortia like OASIS-related activities. Revisions and maintenance involve stakeholders from ISO, national bodies like BSI, AFNOR, DIN, and corporate contributors including Siemens, Dassault Systèmes and PTC (company). The specification has been updated to interoperate with newer APs such as AP242 and to support long-term data retention mandates from agencies including NASA and European Space Agency.

Use Cases and Industry Adoption

Part 21 is widely used for cross-vendor CAD exchange in supply chains for Boeing and Airbus, model archival in repositories at Smithsonian Institution and National Archives and Records Administration, manufacturing workflows in plants of Toyota and BMW, and interoperability during joint ventures like programs between Rolls-Royce and GE Aviation. It appears in data migration projects at Siemens Energy, digital twin deployments by ABB and Schneider Electric, and collaborative engineering consortia such as buildingSMART International and POSC Caesar Association where integration with ISO 10303-242 and PLM systems is essential.

Category:Standards