ISO 10303 - Structure

Structure

STEP is divided into many parts, grouped into

• Environment
  • Parts 1x: Description methods: EXPRESS, EXPRESS-X
  • Parts 2x: Implementation methods: STEP-File, STEP-XML, SDAI
  • Parts 3x: Conformance testing methodology and framework
• Integrated data models
  • The Integrated Resources (IR), consisting of
    • Parts 4x and 5x: Integrated generic resources
    • Parts 1xx: Integrated application resources
    • PLIB ISO 13584-20 Parts library: Logical model of expressions
  • Parts 5xx: Application Integrated Constructs (AIC)
  • Parts 1xxx: Application Modules (AM)
• Top parts
  • Parts 2xx: Application Protocols (AP)
  • Parts 3xx: Abstract Test Suites (ATS) for APs
  • Parts 4xx: Implementation modules for APs

In total STEP consists of several hundred parts and every year new parts are added or new revisions of older parts are released. This makes STEP the biggest standard within ISO. Each part has its own scope and introduction

The APs are the top parts. They cover a particular application and industry domain and hence are most relevant for users of STEP. Every AP defines one or several Conformance Classes, suitable for a particular kind of product or data exchange scenario. To provide a better understanding of the scope, information requirements and usage scenarios an informative application activity model (AAM) is added to every AP, using IDEF0

STEP is primarily defining data models using the EXPRESS modeling language. Application data according to a given data model can be exchanged either by a STEP-File, STEP-XML or via shared database access using SDAI.

Every AP defines a top data models to be used for data exchange, called the Application Integrated Model (AIM) or in the case of a modular AP called Module Integrated Models (MIM). These integrated models are constructed by choosing generic objects defined in lower level data models (4x, 5x, 1xx, 5xx) and adding specializations needed for the particular application domain of the AP. The common generic data models are the basis for interoperability between APs for different kinds of industries and life cycle stages.

In APs with several Conformance Classes the top data model is divided into subsets, one for each Conformance Class. The requirements of a conformant STEP application are:

• implementation of either a preprocessor or a postprocessor or both,
• using one of the STEP implementation methods STEP-File, STEP-XML or SDAI for the AIM/MIM data model and
• supporting one or several conformance classes of an AP.

Originally every APs was required to have a companion Abstract test suite (ATS) (e.g. ATS 303 for AP 203), providing Test Purposes, Verdict Criteria and Abstract Test Cases together with example STEP-Files. But because the development of an ATS was very expensive and inefficient this requirement was dropped and replaced by the requirements to have an informal validation report and recommended practises how to use it. Today the recommended practises are a primary source for those going to implement STEP.

The Application Reference Models (ARM) is the mediator between the AAM and the AIM/MIM. Originally its purpose was only to document high level application objects and the basic relations between them. IDEF1X diagrams documented the AP of early APs in an informal way. The ARM objects, their attributes and relations are mapped to the AIM so that it is possible to implement an AP. As APs got more and more complex formal methods were needed to document the ARM and so EXPRESS which was originally only developed for the AIM was also used for the ARM. Over time these ARM models got very detailed till to the point that some implementations preferred to use the ARM instead of the formally required AIM/MIM. Today a few APs have ARM based exchange formats standardized outside of ISO TC184/SC4:

• PLM-Services within the OMG for AP 214
• ISO 14649 Data model for computerized numerical controllers for AP 238
• PLCS-DEXs within OASIS (organization) for AP 239

There is a bigger overlap between APs because they often need to refer to the same kind of products, product structures, geometry and more. And because APs are developed by different groups of people it was always an issue to ensure interoperability between APs on a higher level. The Application integrated constructs (AIC) solved this problem for common specializations of generic concepts, primarily in the geometric area. To address the problem of harmonizing the ARM models and their mapping to the AIM the STEP modules were introduced. They contain a piece of the ARM, the mapping and a piece of the AIM, called MIM. Modules are built on each other, resulting in an (almost) directed graph with the AP and conformance class modules at the very top. The modular APs are:

• AP 203, Configuration controlled 3D design, TS and 2nd edition
• AP 209, Composite and metallic structural analysis and related design
• AP 210, Electronic assembly, interconnect and packaging design
• AP 221, Functional data and schematic representation of process plants
• AP 236, Furniture product data and project data
• AP 239, Product life cycle support
• AP 241, Generic Model for Life Cycle Support of AEC Facilities (planned)
• AP 242, Managed model based 3d engineering (under development)

The modular editions of AP 209 and 210 are explicit extensions of AP 203.