ISO 10303-21
file format
STEP-file is a widely used data exchange form of STEP. ISO 10303 can represent 3D objects in computer-aided design (CAD) and related information. A STEP-file is ASCII text with the format defined in ISO 10303-21 Clear Text Encoding of the Exchange Structure.
ISO 10303-21 defines the encoding mechanism for representing data conforming to a particular schema in the EXPRESS data modeling language specified in ISO 10303-11. A STEP-File is also called p21-File and STEP Physical File. The file extensions .stp and .step indicate that the file contains data conforming to STEP application protocols while the extension .p21 should be used for all other purposes.
The use of ISO 10303-21 is not limited to STEP. The Industry Foundation Classes and earlier CIMSteel Integration Standard (CIS/2) define an EXPRESS schema for building information modeling data and specify ISO 10303-21 as an exchange encoding.
Example
This graph shows the entity instances and the references between them in a file representing a solid model of a cylinder.
History
Some details to take note of:
The first edition, ISO 10303-21:1994, had some bugs, which were corrected by a Technical Corrigendum. Therefore, it is recommended that users study the second edition instead (see below).
The second edition, ISO 10303-21:2002, included the corrigendum and extensions for several data sections.
Begin with the source’s own compact description: “ISO 10303-21” is file format. The dossier treats that line as a proposition to test through 10303-21, file and format, not as a finished interpretation.
Why this record matters
The phrase “file format” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jul 29, 2026. The linked authority identifier is Q3509055. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1994 and 2002.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
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- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “ISO 10303-21”, its source revision and the description used here.
- Expand the search: follow ISO 10303-21 primary sources, ISO 10303-21 archive and 10303-21 research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “ISO 10303-21”?
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- Which cited source is closest to the event, object or claim?
Search terms from this dossier
This entry incorporates text from “ISO 10303-21” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.