Within the ISO TC184/SC4 suite of standards, STEP has a special role. It is a user-driven standardization initiative that has been going on since early 1980. STEP defines both a methodology - comprising description, implementation and quality methods, and a standard - comprising the application protocols and generic resources.

Application protocols and generic resources are formal specification of information requirements pertinent to a particular industrial and business sector. For interoperability (data exchange) between application protocols, these requirements are mapped to a well-defined set of generic resources.

The EXPRESS information specification language – as part of the descriptive methods defines information requirements in the application protocols. EXPRESS has both a lexical, complete notation intended for implementation, and a graphical, partial notation that mainly are used for presenting information. EXPRESS-I is a formal language for specifying instances to an EXPRESS schema. EXPRESS-X  is for specifying views of and mapping of instances between EXPRESS models. It might also be referred to as a STEP database controlling language.

Implementation methods specify how to access application instance data defined according to an EXPRESS schema. Currently there are two implementation forms: STEP physical file - designed for file based data exchange, and Standard Data Access Interface (SDAI) designed for access to a working form or database.

Quality methods are specifications on how to certify that software complies with the requirements in the application protocols. Abstract test suites may be provided for each application protocol, to ease the work of certifying individual software.

THE OTHER SC4 STANDARDS WILL USE THE STEP METHODOLOGY THAT FOR THIS REASON IS REFERRED TO AS THE SC4 METHODOLOGY.

STEP is a colloquial name for the international standard with the designation ISO 10303, which specifies requirements for data representation and exchange. It is not a monolithic standard but one comprising of many independently managed parts. Each part is classified under one of four major classes: application protocols, generic resources, description methods and implementation methods.

To recapitulate, STEP is comprised of a set of ISO standards, which provide for the exchange of engineering product data. These standards can be grouped into infrastructure components and industry specific information models:

• The EXPRESS information modeling language (Part 11)
• An EXPRESS-driven data exchange file specification (Part 21)
• An EXPRESS-driven application programming interface (SDAI) with bindings to the C, C++, and IDL languages (Parts 22-26)
• A conformance testing framework (Part 31)
• A library of general purpose information models for things like geometry, topology, product identification, dates, times, etc. (The 40-series parts)
• Industry-specific application protocols that are built from the library of general models (the 200-series parts):
  

  • Explicit Drafting (Part 201)

  • Associative Drafting (Part 202)

  • Configuration Controlled Design (Part 203)

  • Automotive Design (Part 214)

  • Many others (Electrical, Shipbuilding, Sheet Metal, etc.)

Other PDT standards

Many PDT standards - not part of SC4, are either using part of or whole of the SC4 methodology for information requirement specification and implementation.