STEP-File is the most widely used data exchange form of STEP. ISO 10303 can represent 3D objects in Computer-aided design (CAD) and related information. Due to its ASCII structure a STEP-file is easy to read with typically one instance per line. The format of a STEP-File is 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.
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