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A New Philosophy for STEP Implementation - STEP for the Web (S4W). David Price October 2003. STEP for Web philosophy, not religion. There is a *philosophy underlying this discussion SC4 made a first foray into “the Web” and replaced EXPRESS/P21 with DTD/XML

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A New Philosophy for STEP Implementation - STEP for the Web (S4W)

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A New Philosophy for STEP Implementation- STEP for the Web (S4W)

David Price

October 2003

STEP for Web philosophy, not religion

  • There is a *philosophy underlying this discussion

    • SC4 made a first foray into “the Web” and replaced EXPRESS/P21 with DTD/XML

      • We got free tools and a bigger pool of programmers

      • However, lots of other new capabilities were missed because SC4 cares about the “pretty-ness” of the XML (and still does)

    • The new S4W philosophy says… SC4 has been missing the forest for the trees

      • What is important is what new capabilities the XML enables

        *Caveat : This philosophy doesn’t do calculus, so it’s not to be applied everywhere

The new S4W philosophy

  • SC4 should focus on putting the semantics of its schemas/data into the forms new Web capabilities use

    • Practically speaking, this means others control the XML

    • However, by giving up control, implementors gain the use of new toolkits and capabilities

    • This may also result in several XML representations of the same schema/data… but that’s OK! Each has a purpose.

    • So, under this philosophy the verbose OWL syntax is far superior to any Part 28 configuration

Part 25, UML and exff

  • Part 25 fits under this philosophy

  • Translating EXPRESS to UML means implementors can use powerful software engineering systems

    • Lowers the cost of STEP implementation

    • Enables use of languages SC4 standards don’t support (e.g. Ada, Smalltalk, OWL)

    • We benefit by giving up some level of control

  • In support of this philosophy, Eurostep has started an open-source project called “exPRESS for free”

exff Problem Statement

  • While it's true that

    • STEP and EXPRESS have been in-work 10-15 years or more, and

    • STEP has saved organizations time and money

  • It's also true that

    • STEP and EXPRESS have not "taken off" the way UML and XML have in recent years

    • In many ways, STEP was ahead of its time

    • As things stand today, there are many good STEP models that will not be widely used

exff Architecture

Software development tools

Engineering application




application code,

database, web service,

knowledge base, …







exff Architecture Details



Project File

U to E


EXPRESS schema

in XML according

to Modules Repository

E to U




UML model in

XML according

to XMI standard







Possible EXPRESS/UML Evolution

  • UML = SDAI for implementors (Part 25)

    • Treat UML as just another language like SDAI/C++

  • UML = EXPRESS-G for modellers (exff)

    • Use UML diagrams instead of EXPRESS-G with no effect on EXPRESS

    • Could satisfy the need for EXPRESS 3 Operations, etc.

  • UML = EXPRESS interoperability for all (E 3?)

    • make them "the same", modellers and implementors use whatever suits them


  • S4W provides huge opportunities for STEP implementation

  • SC4 should focus on the “semantics” that have been agree internationally over the past 15 years

    • However, SC4 should give up control of many aspects of the standards involved during implementation

  • SC4 should formally adopt OMG and W3C standards for implementation and “interoperate” for modelling where ever possible

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