Welcome to the exff Pages

1. Why create "exPRESS for free"?
   • In the Web'ed world, an important aspect of the acceptance of any information technology is the availability of free specifications, reference implementations, and other resources on the Web. exff is aimed at creating these for ISO EXPRESS and at linking that language with related, widespread technologies.
2. What is the scope of exff?
   • The scope of what the exff Project aims to address is broad. Any kind of software or documentation supporting the integration of EXPRESS, UML and IDEs fits within exff. Any kind of software or documentation supporting modelling or implementation based around the core of the exff infrastructure (UML XMI and the EXPRESS XML representation) fits within exff. This includes reference implementations of any UML-, XMI- or EXPRESS-related standards.
3. Who will benefit from exff?
   • The intitial direct benefits of exff apply to those interested in building engineering applications that support or are based around models written using EXPRESS. Integrating EXPRESS into widespread software development tools lowers the cost of the development and broadens the available pool of potential developers.
4. What are the components of exff?
   • The major components of an exff environment, not all of which are available yet, are:
     • UML modelling software;
     • EXPRESS modelling software;
     • a software engineering environment - typically either UML modelling tool plug-ins or a separate IDE that:
       • generates code in various programming languages;
       • generates database and data structure definitions;
       • generates APIs for GUI and data access development;
     • the exff infrastructure which ties the IDE, UML and EXPRESS tools together; and
     • exff-specific plug-ins supporting generation from UML and/or EXPRESS (e.g. ISO Part 21 support);
     • exff-specific tools, or links to existing tools, for schema/model documentation.
5. What is EXPRESS?
   • EXPRESS is an ISO standard "data specification language" used in the STEP series of Industrial Data standards and elsewhere. EXPRESS is functionally equivalent to UML static class diagrams. In some usage scenarios, EXPRESS plays a role similar to that of an XML Schema or DTD.
6. What is UML?
   • UML is the Unified Modeling Language standardized by OMG. See the OMG explanation of UML.
7. What is XMI?
   • XMI is the XML Metadata Interchange standard produced by OMG. With respect to exff, it standardizes the representation of UML models in XML.
8. Where did the EXPRESS XML representation come from?
   • The DTD for the XML representation of EXPRESS schemas used within exff was developed as part of a project for producing ISO Industrial Data standard documents that contain EXPRESS schemas. That project is called stepmod - the STEP Modules Repository.
9. Why wasn't the Part 28 EXPRESS DTD used?
   • ISO 10303-28 standardized a DTD for the EXPRESS language. This DTD was not used for exff because of a difference in design goals. The stepmod DTD is simpler and was designed for the purpose of the production of documentation. It aligns better with the meta-model of UML used with XMI. The Part 28 DTD is based on the syntax of EXPRESS and breaks expressions down into their consituent terms. The UML XMI DTD and the stepmod DTD do not. Lovers of Part 28 should contribute a stepmod DTD-Part 28 EXPRESS DTD translator to exff!
10. Which UML tools will exff support?
    • Any UML tools supporting the OMG XMI standard for model interchange. Some tools support XMI as their native format and others support XMI through an import/export capability. As necessary, the flavors of XMI in specific UML tools will also be supported. The exff goal is interoperability, not necessarily conformance to standards.