STEP parts

The STEP standard consists of the parts listed below. Parts listed in bold characters are the most relevant for understanding STEP as a whole.

Description methods

  • Part 1 (IS): Overview and fundamental principles (1994). Unfortunately outdated, not covering the role of AICs and modules.
  • Part 11 (IS): EXPRESS language reference manual
  • Part 12 (TR): EXPRESS-I language reference manual
  • Part 14 (DIS): EXPRESS-X language reference manual

Implementation methods

  • Part 21 (IS): Clear text encoding of the exchange structure
  • Part 22 (IS): Standard data access interface specification
  • Part 23 (IS): C++ language binding of the standard data access interface
  • Part 24 (IS): C language binding of the standard data access interface
  • Part 25 (CD-TS): EXPRESS to OMG XMI binding
  • Part 27 (TS): Java TM programming language binding to the standard data access interface with Internet/Intranet extensions
  • Part 28 (TS): XML representation for EXPRESS-driven data

Conformance testing methodology and framework

  • Part 31 (IS): General concepts
  • Part 32 (IS): Requirements on testing laboratories and clients
  • Part 34 (IS): Abstract test methods for application protocol implementations
  • Part 35 (TS): Abstract test methods for SDAI implementations

Integrated generic resources

  • Part 41 (IS): Fundamentals of product description and support
  • Part 42 (IS): Geometric and topological representation
  • Part 43 (IS): Representation structures
  • Part 44 (IS): Product structure configuration
  • Part 45 (IS): Materials
  • Part 46 (IS): Visual presentation
  • Part 47 (IS): Shape variation tolerances
  • Part 49 (IS): Process structures and properties
  • Part 50 (IS): Mathematical constructs
  • Part 51 (DIS): Mathematical description
  • Part 52 (AWI): Mesh-based topology
  • Part 53 (AWI): Numerical analysis
  • Part 54 (DIS): Classification and set theory
  • Part 55 (CD): Procedural and hybrid representation
  • Part 56 (CD): State
  • Part 57 (AWI): Expression extensions
  • Part 58 (AWI): Risk

Integrated application resources

  • Part 101 (IS): Draughting
  • Part 104 (IS): Finite element analysis
  • Part 105 (IS): Kinematics
  • Part 107 (CD): Finite element analysis definition relationships
  • Part 108 (DIS): Parameterization and constraints for explicit geometric product models
  • Part 109 (DIS): STEP assembly model for products
  • Part 110 (AWI): Computational fluid dynamics data

Application Protocol

The 'APs' utilize the lower-level information of integrated resources in well defined combinations and configurations to represent a particular data model of an engineering or technical application.

  • Part 201 (IS): Explicit draughting. Simple 2D drawing geometry related to a product. No association, no assembly hierarchy. Practically a subset of AP202 and 214.
  • Part 202 (IS): Associative draughting. 2D/3D drawing with association, but no product structure. Practically a subset of AP214.
  • Part 203 (IS): Configuration controlled design. Mainly used for 3D design and product structure. A subset of AP214 but most widely used.
  • Part 204 (IS): Mechanical design using boundary representation
  • Part 207 (ID): Sheet metal die planning and design
  • Part 209 (IS): Composite and metallic structural analysis and related design
  • Part 210 (IS): Electronic assembly, interconnect and packaging design. The most complex and sohisticated STEP AP.
  • Part 212 (IS): Electrotechnical design and installation. Designed as a complement for AP214, but not fully harmonized with it.
  • Part 214 (IS): Core data for automotive mechanical design processes
  • Part 215 (DIS): Ship arrangement
  • Part 216 (IS): Ship moulded forms
  • Part 218 (DIS): Ship structures
  • Part 219 (AWI): Dimensional inspection information exchange
  • Part 221 (CD): Functional data and their schematic representation for process plant
  • Part 224 (IS): Mechanical product definition for process plans using machining features
  • Part 225 (IS): Building elements using explicit shape representation
  • Part 227 (IS): Plant spatial configuration
  • Part 232 (IS): Technical data packaging core information and exchange
  • Part 233 (AWI): Systems engineering data representation
  • Part 235 (WD): Materials information for the design and verification of products
  • Part 236 (WD): Furniture product data and project data
  • Part 237 (AWI): Fluid dynamics
  • Part 238 (CD): Application interpreted model for computer numeric controllers
  • Part 239 (AWI): Product life cycle support
  • Part 240 (AWI): Process plans for machined products

ATS - Abstract test suite

An ATS is a formal description on how to test STEP implementations for conformance. They contain a test plan for postprocessors (exporting STEP data) and preprocessors (importing STEP data). The structure of an ATS is defined in part 34.

The original plan of STEP was to have for every AP 2xx a corresponding ATS 3xx. However, ATSs were not very successful. Most AP projects run out of money and had at the end no resources left to develop the corresponding ATS. For some APs an ATS was developed, but it was not finished so that the project got canceled after a while. No ATS is under development today. The few useful ATS developed are 303, 307, 324, and 332.

AIC - Application interpreted constructs

AICs are specializations of the integrated application and generic resources. This is done by subtyping interfaced entities and adding further constraints and rules. No new stand-alone entities are created and no new explicit attributes are added. Most AICs are specializations in the geometric area. AICs did not exist back in 1994 when the first release of STEP got published. But when the 2nd generation of APs grows up it becomes clear that APs share not only the IRs but also a lot of specializations. AICs are a big step towards AP interoperability.

  • Part 501 (IS): Edge-based wireframe
  • Part 502 (IS): Shell-based wireframe
  • Part 503 (IS): Geometrically bounded 2D wireframe
  • Part 504 (IS): Draughting annotation
  • Part 505 (IS): Drawing structure and administration
  • Part 506 (IS): Draughting elements
  • Part 507 (IS): Geometrically bounded surface
  • Part 508 (IS): Non-manifold surface
  • Part 509 (IS): Manifold surface
  • Part 510 (IS): Geometrically bounded wireframe
  • Part 511 (IS): Topologically bounded surface
  • Part 512 (IS): Faceted boundary representation
  • Part 513 (IS): Elementary boundary representation
  • Part 514 (IS): Advanced boundary representation
  • Part 515 (IS): Constructive solid geometry
  • Part 517 (IS): Mechanical design geometric presentation
  • Part 518 (IS): Mechanical design shaded representation
  • Part 519 (IS): Geometric tolerances
  • Part 520 (IS): Associative draughting elements
  • Part 521 (IS): Manifold subsurface
  • Part 522 (IS): Machining features
  • Part 523 (CD): Curve swept solid


A new generation of modularized APs are under development. Their contents (ARM and AIM) is based on modules. These are AP 203 2nd edition, 236, and 239.

  • part 4xx, Application modules
  • Part 1xxx, Basic modules


Not every development of an information model based on STEP technology was done within ISO TC184/SC4 and got published by ISO. This list mentions several of them:

  • NPDM: NATO Product Data Model. This data model covers in great detail the whole product life cycle, including changing configurations of a product over time and failure analysis. It is an implementation proved alternative for AP239.
  • STEP-TAS: Thermal analysis for space. Developed by ESA/ESTEC
  • STEP-NRF: Network model result format. Like STEP-TAS developed by ESA/ESTEC
  • STEP-NC: Data model for computerized numerical controllers, ISO 14649
  • Mecha-STEP: STEP data model for simulation data of mechatronic systems, DIN PAS 1013 (2001)
  • ESPRIT project 6457 - InterRob: A STEP based reference model for exchange of robotics models.; geometrx, kinmatics, dynamics, control, and robotics specific data (1996)
  • Recommendation for a Product Model of Gear units, VDMA 23900 (2003), a specialization of STEP-AP214
  • IFC for building construction

Status of STEP parts

An ISO standard or a part of it grows usually up through several stages:

  • PWI: Preliminary new work item
  • NWI: New work item
  • WD: Working draft
  • CD: Commitee draft
  • DIS: Draft international standard
  • FDIS: Final draft international standard
  • IS: (final) international standard

Not every part of STEP is evolving to an international standard. Some parts got published on a lower level:

  • TR: Technical report
  • PAS: Public available specification. It requires more than 50% of the votes
  • TS: Technical specification. This requires 66% of the votes and is intented to be moved forward to IS at a later time.

Also it is to be mentioned that for several parts technical corrigenda (TC) are available or will become available.