About Express

Express

Express is the language for the specification of conceptual data models used within STEP (Standard for the Exchange of Product data). The Express language is specified as part 11 of the ISO 10303 standard for Product Data and exchange.

STEP and ISO 10303

ISO 10303 ‘Industrial automation systems and integration - Product data representation and exchange’ is an ISO standard for the computer-interpretable representation and exchange of product data. It provides a neutral mechanism capable of describing product data throughout the life cycle of a product independent from any particular system. The nature of his description makes it suitable not only for neutral file exchange, but also as a basis for implementing and sharing product databases and archiving.

The ISO standard 10303 is organised as a series of parts, each published separately. The parts of ISO 10303 fall into one of the following series (see ISO 10303-1):

- description methods	e.g. parts 11 and 12
- integrated generic resources	e.g. parts 41 - 49
- integrated application resources	e.g. parts 101 - 105
- application protocols	e.g. parts 201 - 213
- abstract test suites
- implementation methods	e.g. parts 21 and 22
- conformance testing	e.g. parts 31 and 32

Part 21 ‘Implementation methods - Clear text encoding of the exchange structure’ defines a standard the exchange of data based on Express specifications. The part 21 exchange format is often called the "e;STEP file format"e;.

Part 22 - 24 specify standard data access interfaces (SDAIs), application program interfaces for C++, C, Fortran and Lisp to access date based on the Express specifications.

The Express Language

Express is the name of a formal information requirements specification language. It is based on a number of design goals among which are:

• the size and complexity of the specifications demand that the language be parsable by both computers and humans. If the specifications where expressed in a less formal manner, it would eliminate the possibility of employing computer automation in checking for inconsistencies in presentation or for creating any number of secondary views, including implementation views.
• Express is designed to enable partitioning of diverse material addressed by ISO 10303. The schema is the basis for partitioning and interconnection and intercommunication.
• Express focuses on the definition of entities, which represent objects of interest. The definition of an entity is in terms of its properties, which are characterised by specification of a domain and the constraints on that domain.
• Express seeks to avoid, as far as possible, implementation views. However, it is possible to manufacture implementation views (such as static file exchange) in an automatic and straightforward manner.

Reasons to use Express for the specification of conceptual data models

Using Express for the description of conceptual data models has several advantages:

• it supports both a lexical as well as graphical (Express-G) representation,
  while the graphical representation provides a quick overview, the lexical representation allows for details, like al kinds of constraints;
• readability,
  Express and Express-G specifications are relatively easy to read.
• as Express is formally defined, the Express concepts have a precise meaning
• manageable descriptions, even for very complex structures,
  Express may be used to specify very complex data structures and, because of the schema construct, configuration management is relatively easy.
• Express is used in related areas
  e.g. to describe geographic  information, and in the construction and automotive industry.

Additional Information

• Express (Wikipedia article on Express)
• EPM (Home page of EPM Technology a.s.,the supplier of the Express tool used)
• StepTools (home page of StepTools, another supplier of Express tools)
• CEN TC287 (Home page CEN Technical Committee 'Geographic Information')
• CEN TC287 standards  (CEN Technical Committee 'Geographic Information', list of standards)
• ISO (International Standard Organisation)
• For a book about Express see e.g.:
  Schenk, Douglas A. and Wilson, Peter R.,  Information Modelling : The Express way,
  Oxford University Press,  ISBN 0-19-508714-3