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ISO 10303 is an ISO standard for the computer-interpretable representation and exchange of product manufacturing information. It is an ASCII-based format.[1]: 59  Its official title is: Automation systems and integration — Product data representation and exchange. It is known informally as "STEP", which stands for "Standard for the Exchange of Product model data". ISO 10303 can represent 3D objects in Computer-aided design (CAD) and related information.


The objective of the international standard is to provide a mechanism that is capable of describing product data throughout the life cycle of a product, independent from any particular system. The nature of this description makes it suitable not only for neutral file exchange, but also as a basis for implementing and sharing product databases and archiving.[2]

STEP can be typically used to exchange data between CAD, computer-aided manufacturing, computer-aided engineering, product data management/enterprise data modeling and other CAx systems. STEP addresses product data from mechanical and electrical design, geometric dimensioning and tolerancing, analysis and manufacturing, as well as additional information specific to various industries such as automotive, aerospace, building construction, ship, oil and gas, process plants and others.

STEP is developed and maintained by the ISO technical committee TC 184, Automation systems and integration, sub-committee SC 4, Industrial data. Like other ISO and IEC standards STEP is copyright by ISO and is not freely available. However, the 10303 EXPRESS schemas are freely available, as are the recommended practices for implementers.

Other standards developed and maintained by ISO TC 184/SC 4 are:[3]

STEP is closely related with PLIB (ISO 13584, IEC 61360).


The basis for STEP was the Product Data Exchange Specification (PDES), which was initiated during the mid-1980's and was submitted to ISO in 1988.[4][5] The Product Data Exchange Specification (PDES) was a data definition effort intended to improve interoperability between manufacturing companies, and thereby improve productivity.[6]

The evolution of STEP can be divided into four release phases. The development of STEP started in 1984 as a successor of IGES, SET and VDA-FS.[7] The initial plan was that "STEP shall be based on one single, complete, implementation-independent Product Information Model, which shall be the Master Record of the integrated topical and application information models".[8] But because of the complexity, the standard had to be broken up into smaller parts that can be developed, balloted and approved separately.[9] In 1994/95 ISO published the initial release of STEP as international standards (IS) with the parts 1, 11, 21, 31, 41, 42, 43, 44, 46, 101, AP 201 and AP 203.[10] Today AP 203 Configuration controlled 3D design is still one of the most important parts of STEP and supported by many CAD systems for import and export.

In the second phase the capabilities of STEP were widely extended, primarily for the design of products in the aerospace, automotive, electrical, electronic, and other industries. This phase ended in the year 2002 with the second major release, including the STEP parts AP 202, AP 209, AP 210, AP 212, AP 214, AP 224, AP 225, AP 227, AP 232.[11] Basic harmonization between the APs especially in the geometric areas was achieved by introducing the Application Interpreted Constructs (AIC, 500 series).[12]

A major problem with the monolithic APs of the first and second releases is that they are too big, have too much overlap with each other, and are not sufficiently harmonized. These deficits led to the development of the STEP modular architecture (400 and 1000 series).[13][12] This activity was primarily driven by new APs covering additional life-cycle phases such as early requirement analysis (AP 233) and maintenance and repair (AP 239), and also new industrial areas (AP 221, AP 236). New editions of the previous monolithic APs on a modular basis have been developed (AP 203, AP 209, AP 210). The publication of these new editions coincided with the release in 2010 of the new ISO product SMRL, the STEP Module and Resource Library, that contains all STEP resource parts and application modules on a single CD. The SMRL will be revised frequently and is available at a much lower cost than purchasing all the parts separately.

In December 2014, ISO published the first edition of a new major Application Protocol, AP 242 Managed model based 3d engineering, that combined and replaced the following previous APs in an upward compatible way:

AP 242 was created by merging the following two Application protocols:

In addition AP 242 edition 1 contains extensions and significant updates for:

Two APs had been modified to be directly based on AP 242, and thus became supersets of it:

AP242 edition 2, published in April 2020, extends edition 1 domain by the description of Electrical Wire Harnesses and introduces an extension of STEP modelisation and implementation methods based on SysML and system engineering with an optimized XML implementation method.

This new edition contains also enhancements on 3D Dimensioning and Tolerancing, and Composite Design. New functionalities are also introduced like:


Main article: List of STEP (ISO 10303) parts

STEP is divided into many parts, grouped into

In total STEP consists of several hundred parts and every year new parts are added or new revisions of older parts are released. This makes STEP the biggest standard within ISO. Each part has its own scope and introduction.

The APs are the top parts. They cover a particular application and industry domain and hence are most relevant for users of STEP. Every AP defines one or several Conformance Classes, suitable for a particular kind of product or data exchange scenario. To provide a better understanding of the scope, information requirements and usage scenarios an informative application activity model (AAM) is added to every AP, using IDEF0.

STEP is primarily defining data models using the EXPRESS modeling language. Application data according to a given data model can be exchanged either by a STEP-File, STEP-XML or via shared database access using SDAI.

Every AP defines a top data models to be used for data exchange, called the Application Interpreted Model (AIM) or in the case of a modular AP called Module Interpreted Models (MIM). These interpreted models are constructed by choosing generic objects defined in lower level data models (4x, 5x, 1xx, 5xx) and adding specializations needed for the particular application domain of the AP. The common generic data models are the basis for interoperability between APs for different kinds of industries and life cycle stages.

In APs with several Conformance Classes the top data model is divided into subsets, one for each Conformance Class. The requirements of a conformant STEP application are:

Originally every APs was required to have a companion Abstract test suite (ATS) (e.g. ATS 303 for AP 203), providing Test Purposes, Verdict Criteria and Abstract Test Cases together with example STEP-Files. But because the development of an ATS was very expensive and inefficient this requirement was dropped and replaced by the requirements to have an informal validation report and recommended practices how to use it. Today the recommended practices are a primary source for those going to implement STEP.

The Application Reference Models (ARM) is the mediator between the AAM and the AIM/MIM. Originally its purpose was only to document high level application objects and the basic relations between them. IDEF1X diagrams documented the AP of early APs in an informal way. The ARM objects, their attributes and relations are mapped to the AIM so that it is possible to implement an AP. As APs got more and more complex formal methods were needed to document the ARM and so EXPRESS which was originally only developed for the AIM was also used for the ARM. Over time these ARM models got very detailed till to the point that some implementations preferred to use the ARM instead of the formally required AIM/MIM. Today a few APs have ARM based exchange formats standardized outside of ISO TC184/SC4:

There is a bigger overlap between APs because they often need to refer to the same kind of products, product structures, geometry and more. And because APs are developed by different groups of people it was always an issue to ensure interoperability between APs on a higher level. The Application Interpreted Constructs (AIC) solved this problem for common specializations of generic concepts, primarily in the geometric area. To address the problem of harmonizing the ARM models and their mapping to the AIM the STEP modules were introduced. They contain a piece of the ARM, the mapping and a piece of the AIM, called MIM. Modules are built on each other, resulting in an (almost) directed graph with the AP and conformance class modules at the very top. The modular APs are:

The modular editions of AP 209 and 210 are explicit extensions of AP 242.

Coverage of STEP Application Protocols (AP)

The STEP APs can be roughly grouped into the three main areas design, manufacturing and life cycle support.

Design APs:

Manufacturing APs:

Life cycle support APs:

The AP 221 model is very similar to the ISO 15926-2 model, whereas AP 221 follows the STEP architecture and ISO 15926-2 has a different architecture. They both use ISO-15926-4 as their common reference data library or dictionary of standard instances. A further development of both standards resulted in Gellish English as general product modeling language that is application domain independent and that is proposed as a work item (NWI) for a new standard.

The original intent of STEP was to publish one integrated data-model for all life cycle aspects. But due to the complexity, different groups of developers and different speed in the development processes, the splitting into several APs was needed. But this splitting made it difficult to ensure that APs are interoperable in overlapping areas. Main areas of harmonization are:

For complex areas it is clear that more than one APs are needed to cover all major aspects:

See also


  1. ^ Schoonmaker, Stephen J. (2003). The CAD guidebook : a basic manual for understanding and improving computer-aided design. New York: Marcel Dekker. ISBN 0-8247-4569-8. OCLC 54090798.
  2. ^ ISO 10303-1:1994 Industrial automation systems and integration -- Product data representation and exchange -- Part 1: Overview and fundamental principles
  3. ^ Standards and projects under the direct responsibility of ISO/TC 184/SC 4 Secretariat [1]
  4. ^ Kutz, Myer (22 Jul 2002). Handbook of Materials Selection. John Wiley & Sons. p. 498. ISBN 9780471359241. The IGES/PDES Organization was coordinated in the late 1970s from industry, government, and academia to develop standards and technology for the exchange of product information between different CAD systems. This group focused its efforts on two projects, the Initial Graphics Exchange Specification (IGES) and the Product Data Exchange Specification (PDES) using STEP. This effort resulted in the publication of IGES in 1980, which was subsequently adopted as an ANSI standard. ... A second-generation Product Data Exchange (PDE) technology, Product Data Exchange Specification (PDES), was initiated during the mid-1980s and was submitted to ISO in 1988. The international community adopted it as the basis for ISO 10303 (STEP). Today, the ongoing PDE technology efforts include the Product Data Exchange using STEP (PDES), an American National Standard (ANS). This project is the primary U.S. project providing industry inputs into this ISO activity. Fourteen international standards have been created as a result of this effort. More than 20 countries worldwide have approved STEP, including all major U.S. trading partners.
  5. ^ Kemmerer, Sharon, ed. (October 1, 1999). STEP: The Grand Experience. Gaithersburg, MD: NIST Special Publication 939. doi:10.6028/NIST.SP.939.
  6. ^ Powers 2003, p. 9.
  7. ^ ISO TC184 / SC4 resolution 1, Gaithersburg - July 1984
  8. ^ ISO TC184 / SC4 resolution 33, Tokyo - December 1988
  9. ^ ISO TC184 / SC4 resolution 55, Paris - January 1990
  10. ^ ISO TC184 / SC4 resolution 195 and 196, Davos - May 1994
  11. ^ ISO TC184 / SC4 resolution 361, Bad Aibling, Germany – June 1998
  12. ^ a b Feeney, Allison Barnard (2002-06-01). "The STEP Modular Architecture". Journal of Computing and Information Science in Engineering. 2 (2): 132–135. doi:10.1115/1.1511520. ISSN 1530-9827.
  13. ^ ISO TC184 / SC4 resolution 394, San Francisco, California - January 1999


STEP programs