STEPFile

STEPFile is a file format for exchanging 3D product data that follows ISO 10303, the STEP standard. Files typically use the extensions .step or .stp and can encode geometry, topology, assembly structure, and product metadata. STEPFile data is commonly stored in ASCII text, though XML encodings exist as well.

The ASCII representation of STEPFile is defined in ISO 10303-21. A STEPFile contains a header and a data section. The header includes FILE_DESCRIPTION, FILE_NAME, and FILE_SCHEMA. The data section contains a sequence of entity instances identified by numeric IDs (for example, #12 = CARTESIAN_POINT(...);). Data records describe geometry, topology, and assemblies under an Application Protocol such as AP203 or AP214.

Application protocols specify the domain model conveyed by the file; AP203 targets configuration-controlled 3D designs, AP214 supports automotive and product lifecycle data, among others. The chosen AP determines which entities and relationships appear in the file. There is also STEP-XML, an XML encoding defined by ISO 10303-28, but STEPFile remains more widely supported.

Usage and interoperability: STEPFile enables data exchange between CAD, PLM, and CAE tools to support long-term data retention. Real-world fidelity can vary, and some complex features may require post-processing to preserve semantics during translation. Open-source and commercial libraries, such as OpenCASCADE and STEPcode, provide STEPFile readers and writers.