STEP-File is the most widely used[citation needed] data exchange form of STEP. ISO 10303 can represent 3D objects in Computer-aided design (CAD) and related information. Due to its ASCII structure it 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.[1]
ISO 10303-21 defines the encoding mechanism on how to represent data according to a given EXPRESS schema, but not the EXPRESS schema itself. A STEP-File is also called p21-File and STEP Physical File. The file extensions .stp and .step indicates that the file contain data conforming to STEP Application Protocols while the extension .p21 should be used for all other purposes.[2]
