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The STEP Standard

The STandard for the Exchange of Product model data (STEP) is currently being developed by the International Organization for Standardization (ISO). It is intended to contain the unambiguous representation of product data throughout the entire life cycle of a product.

The unique feature of STEP is that it integrates product data. In today's environment, the data for a product is managed in many different systems with little integration and with data redundancy. The data redundancy is primarily caused by the lack of integration. Data must be replicated from system to system in order to maintain a correlation between the systems. STEP proposes to alleviate this problem by providing a single product data storage standard which integrates the data.

Levels of Implementation

The STEP standard does not intend to standardize how an enterprise gets its data into the standard representation. The intention is to provide a migration path. The migration path is described by the levels of implementation of STEP. These levels are:

Level 1- Passive File

Level 2- Active File

Level 3- Database

Level 4- Knowledge Base

The passive file exchange is a flat ASCII file which contains the STEP data. This level is basically translator based. The active file is a memory resident image of the STEP data which can be used interactively by applications. The database implementation level provides additional facilities whereby applications can be constructed that take views of the data which are different than the native storage format, and support relational, network, hierarchical and object oriented types of queries. The knowledge base implementation stores the data as objects complete with attached constraint rules from the STEP standard. The first three levels of implementation can not attach rules to entities and attributes without the use of application code even though these rules can be and are defined in the standard.

STEP can be somewhat directly implemented. The standard is written in the EXPRESS language that was developed for the purpose of allowing the standard to be human readable and computer interpretable. This means that programs can be written to use the standard as input. The standard defines the data structure and the rules for data storage. A program can read the standard and determine the data storage structure. The program can also be provided with mappings between STEP entities and attributes to an application's entities and attributes. This structure allows for complete restructure with a minimum of programming effort. This is especially true when entities and attributes are added, modified or deleted from the standard.

EXPRESS is designed to be implementation independent and thus support the four levels of implementation defined for STEP to date. It defines a common interpretation of the standard in terms of data and rules. This common interpretation can be used to drive computer processes. In order to do so, both the data definitions and the rules must be implemented. In levels 1 through 3, the data definitions can be used to define mappings to other applications or between versions of the standard. In level 4, this can be extended to where not only data can be mapped, but processing requirements (in the form of EXPRESS local and global rules) and complex relationships can be checked and enforced without additional programming effort.

EXPRESS has a number of dialects which are:

• EXPRESS-C EXPRESS with static and behavioural modelling capabilities
• EXPRESS-G Graphical language
• EXPRESS-I Instantiation language
• EXPRESS-M Mapping definition language
• EXPRESS-P Process definition language
• EXPRESS-V Extension of EXPRESS which enables the creation of views
• EXPRESS-X Merger of M and V

The overall structure of the standard is summarized here which is also known as STEP On A Page. In words, the basic breakdown is:

• Parts 11 to 19 specify the Description methods,
• Parts 21 to 29 specify the Implementation methods,
• Parts 31 to 39 specify the Conformance testing methodology and framework,
• Parts 41 to 99 specify the Integrated generic resources,
• Parts 101 to 199 specify the Integrated application resources,
• Parts 201 to 299 specify the Application protocols,
• Parts 301 to 399 specify the Abstract test suites, and
• Parts 501 to 599 specify the Application interpreted constructs

Further information on all these parts and their current status can be found here.

Application Protocols

The piece of STEP which actually gets implemented, exchanged, or shared is the Application Protocols. Here is some various information on some of these:

• Part 201: Explicit draughting
• Part 202: Associative draughting
• Part 203: Configuration controlled design
• Part 204: Mechanical design using boundary representation
• Part 205: Mechanical design using surface representation
• Part 207: Sheet metal die planning and design
• Part 208: Life cycle management - Change process
• Part 209: Composite and metallic structural analysis and related design
• Part 210: Electronic assembly, interconnect and packaging design
• Part 212: Electrotechnical design and installation
• Part 213: Numerical control process plans for machined parts
• Part 214: Core Data for Automotive Mechanical Design Processes
• Part 215: Ship arrangement
• Part 216: Ship moulded forms
• Part 217: Ship piping
• Part 218: Ship structures
• Part 220: Process planning, manufacture, and assembly of layered electronic products
• Part 221: Functional data and their schematic representation for process plant
• Part 222: Exchange of product data for composite structures
• Part 223: Exchange of design and manufacturing product information for casting parts
• Part 224: Mechanical product definition for process plans using machining features
• Part 225: Building elements using explicit shape representation
• Part 226: Ship mechanical systems
• Part 227: Plant spatial configuration
• Part 230: Building structural frame: Steelwork
• Part 231: Process engineering data: Process design and process specification of major equipment
• Part 232: Technical data packaging core information and exchange
• Part 233: Systems Engineering Application Protocol
• Part 234: Ship Operational Logs, Records, and Messages

Application protocols can be implemented via flat/ physical file translators via STEP Part 21 or via the Standard Data Access Interface (SDAI).

STEP vs Other Standards

An important question to ask when considering the implementation of STEP is: Why should my company move to STEP rather than continue using existing accepted standards?

This is an important question. Existing standards, their implementation and use can provide some interesting bench marks with which to compare STEP. There is an important difference between STEP and most other standards. The difference is that most other standards deal only with particular application areas or particular deliverables or products. STEP is intended to store all data for a product throughout its life-cycle with out regard to discipline or application area.

STEP is an international standard. This designation gives STEP a distinct advantage over company, industry, and national standards for companies in today's economy. STEP data can be exchanged and shared across international boundaries. This means that products designed in one country could be produced anywhere in the world.

STEP is intended to deal with all types of products and all data related to those products. It also forces the integration of product data. This integration is a very distinguishing feature of STEP. No other standard currently offers this capability. This feature is very important to consider when evaluating STEP. Standards which do not provide this integration provide benefits only if data is reused. The integration provided in STEP can be an important advantage even if data is never exchanged. Integration of data and the systems that deal with that data eliminates or at least severely reduces redundancy. This eliminates the need for tasks required to support the redundancy.