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STEP(5)			 BRL-CAD Format	Documentation		       STEP(5)

NAME
       STEP - ISO 10303	Standard for the Exchange of Product model data

BACKGROUND
       In 1984,	the International Organization for Standardization (ISO) began
       working to create a standard to allow for the electronic	exchange of
       product data between computer-based product life-cycle systems. This
       scope was intentionally much broader than just geometry information,
       and the resulting standard (ISO 10303: Industrial automation systems
       and integration -- Product data representation and exchange) is
       extremely large.	Consequently, the standard is subdivided into parts,
       which are referred to individually as ISO 10303-xxx where xxx is	the
       part number. Because of the large scope,	there is a numbering
       convention used to represent more focused sub-scopes in order to	make
       locating	specific types of information simpler:

       Table 1.	ISO 10303 Part Numbering Scopes
       +-------+---------------------------+
       |Series | Scope Of Series	   |
       +-------+---------------------------+
       |00x    | Overview, fundamental	   |
       |       | principles		   |
       +-------+---------------------------+
       |01x    | Definitional resources	   |
       +-------+---------------------------+
       |02x    | Implementation	methods	   |
       +-------+---------------------------+
       |03x    | Validation of translators |
       |       | for standard conformance  |
       +-------+---------------------------+
       |04x    | Integrated Generic	   |
       |       | Resources (basic building |
       |       | blocks)		   |
       +-------+---------------------------+
       |1xx    | Integrated Application	   |
       |       | Resources (higher level   |
       |       | than 04x)		   |
       +-------+---------------------------+
       |2xx    | Application Protocols	   |
       +-------+---------------------------+
       |5xx    | Application Interpreted   |
       |       | Constructs - reusable	   |
       |       | components of Application |
       |       | Protocols		   |
       +-------+---------------------------+
       The lowest level	parts that define STEP in a practical sense are	ISO
       10303-011, ISO 10303-21,	and ISO	10303-022. 10303-011 defines the
       EXPRESS language, which is in turn the language in which	application
       protocol	schemas	are written. 10303-21 defines a	clear text encoding of
       the STEP	exchange structure - files using this schema are referred to
       as "STEP" or "Part 21" files. 10303-022 defines a Standard Data Access
       Interface (SDAI)	which is used to automatically generate	practical
       computer	code from the EXPRESS schema protocol descriptions.
       Collectively, these define the "container" aspects of the STEP file
       format and a method to access the information from the file. (This is
       similar to using	XML with a schema file to store	information, and newer
       schemas are also	available in an	XML form in addition to	EXPRESS.)

       A number	of other low level parts and higher level Application
       Interpreted Constructs (AICs) form the foundation on which the more
       complete	"high level" parts are defined.	This separation	is performed
       mainly to allow maximal sharing and compatibility between different
       high level parts	that need the same lower level foundations.

       Within that context, the	primary	components of interest for practical
       data import and export are the Application Protocols (AP) that focus on
       shape models and	assembly structure (among other	things.) The first
       such protocol was AP203 - "Configuration-controlled design". As
       experience using	the standard in	real world applications	accumulated,
       new revisions and new application protocols were	developed. Today, the
       following protocols exist:

       Table 2.	Application Protocols relating to Shape	Modeling and Assembly
       Structure
       +------------+---------------------+---------------------+
       |Application | Title		  | Notes		|
       |Protocol    |			  |			|
       +------------+---------------------+---------------------+
       |AP203	    | Configuration	  | Most recent	version	|
       |	    | controlled 3D	  | is 10303-203:1994	|
       |	    | designs of	  | with additions and	|
       |	    | mechanical parts	  | corrections	as	|
       |	    | and assemblies	  | follows:  the	|
       |	    |			  | original document	|
       |	    |			  | was	subsequently	|
       |	    |			  | revised by one	|
       |	    |			  | amendment		|
       |	    |			  | 10303-203:1994/Amd	|
       |	    |			  | 1:2000 and three	|
       |	    |			  | corrections:	|
       |	    |			  | 10303-203:1994/Cor	|
       |	    |			  | 1:1996,		|
       |	    |			  | 10303-203:1994/Cor	|
       |	    |			  | 2:1998, and		|
       |	    |			  | 10303-203:1994/Cor	|
       |	    |			  | 3:2004.		|
       |	    |			  | 10303-203:2005 is	|
       |	    |			  | considered a	|
       |	    |			  | revision to	this	|
       |	    |			  | standard.		|
       +------------+---------------------+---------------------+
       |AP203e2	    | Configuration	  | Most recent	version	|
       |	    | controlled 3D	  | is 10303-203:2011.	|
       |	    | designs of	  | Revises		|
       |	    | mechanical parts	  | 10303-203:2005,	|
       |	    | and assemblies	  | which is listed as	|
       |	    |			  | a modular version	|
       |	    |			  | that is harmonized	|
       |	    |			  | with ISO 10303-214.	|
       |	    |			  | 10303-242:2014 is	|
       |	    |			  | considered a	|
       |	    |			  | revision to	this	|
       |	    |			  | standard.		|
       +------------+---------------------+---------------------+
       |AP214	    | Core data	for	  | Most recent	version	|
       |	    | automotive	  | is 10303-214:2010	|
       |	    | mechanical design	  | (a.k.a AP214e3).	|
       |	    | processes		  | Two	earlier		|
       |	    |			  | versions exist:	|
       |	    |			  | 10303-214:2003 and	|
       |	    |			  | 10303-214:2001.	|
       |	    |			  | 10303-242:2014 is	|
       |	    |			  | considered a	|
       |	    |			  | revision to	this	|
       |	    |			  | standard.		|
       +------------+---------------------+---------------------+
       |AP242	    | Managed model-based | Most recent	version	|
       |	    | 3D engineering	  | is 10303-242:2014.	|
       |	    |			  | This standard is	|
       |	    |			  | intended to		|
       |	    |			  | consolidate	and	|
       |	    |			  | replace AP203e2 and	|
       |	    |			  | AP214. One		|
       |	    |			  | correction has been	|
       |	    |			  | published:		|
       |	    |			  | 10303-242:2014/Cor	|
       |	    |			  | 1:2016.		|
       +------------+---------------------+---------------------+
       AP203e2 is sufficiently different from AP203 that practically speaking
       it merits being called out as its own distinct protocol,	but in the
       nomenclature of the ISO standards it is still considered	a revision to
       AP203.

       These protocols are the portion of ISO 10303 that address the problem
       domain previously handled by the	Initial	Graphics Exchange
       Specification (IGES(5)).	In a computer aided design context where
       transfer	of "STEP files"	is being discussed, those files	will most
       likely correspond to one	of the previous	protocols.

       TODO - Determine	what MIM, AIM and AAM are and document them...

SCHEMAS	AND IMPLEMENTATION RESOURCES
       To obtain the latest schema files (which, unlike	the ISO	standards
       themselves, are freely available) check the STEP	Module Repository
       Project - in particular,	the modules directory.

       The standards define the	structure of the schemas, but in general when
       it comes	to the nuts and	bolts of implementing a	practical importer and
       exporter	more resources are needed. Below are links to some
       implementation resources:

       PDES, Inc. Industry consortium Recommended Practices for	AP203, April
       1998

       PDM Implementer Forum, Usage Guide for the STEP PDM Schema V1.2 Release
       4.3, January 2002.

       CAx Implementer Forum Recommended Practices:
       https://www.cax-if.org/joint_testing_info.html#recpracs

SEE ALSO
       Pratt, Michael J.; Introduction to ISO 10303 - the STEP Standard	for
       Product Data Exchange; NIST; 2001.

AUTHOR
       Clifford	Yapp

COPYRIGHT
       Copyright (c) 2015-2019 by the United States Government as represented
       by U.S. Army Research Laboratory.

BUG REPORTS
       Reports of inaccuracies should be submitted via electronic mail to
       devs@brlcad.org

BRL-CAD				  08/27/2021			       STEP(5)

NAME | BACKGROUND | SCHEMAS AND IMPLEMENTATION RESOURCES | SEE ALSO | AUTHOR | COPYRIGHT | BUG REPORTS

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