Figure 1: The SGML_STRING
The introduction of the SGML_STRING construct into the STEP resource models is necessary for the integration of the STEP and SGML families of standards. It permits the definition and utilization of SGML text strings as STEP objects. This allows the STEP compliant product models to contain text which can be used to produce SGML documents, e.g., for presentation.
The advantages of the integration will permit users to integrate the documentation of products into the life-cycle of the product itself and the documentation will become just another component of the product, following the life-cycle as any other component. The users of STEP applications will be able to combine SGML text along with the design / manufacturing / production data. For example, the design of a component, such as an airplane wing can be directly coupled to textual information describing any relevant aspects of the design. This information can be added to and modified throughout the componentÕs life cycle. And, at any time in the life cycle, this information can be exported to an SGML environment for publication.
The ability to define SGML ÓproductsÓ in the STEP environment opens up the possibilities of tapping in to the broad spectrum of STEP associated applications, such as advanced modelling, automatic database generation, workflow, versioning, etc.
The SGML_STRING is an information structure defined as an EXPRESS construct (see diagram).
Figure 1: The
SGML_STRING
This structure allows the storing of SGML text as well as providing references to the necessary SGML constructs.
The SGML_STRING includes:
The content of the SGML_STRING is a string (sequence) of character codes. These character codes may include the character codes that SGML recognises as defining mark-up (tags). Since SGML in itself may use any character code set (not limited to ISO 646), the content is of type BINARY.
The SGML_STRING references a DTD fragment which defines any of the mark-up codes found in the SGML_STRING content. As well, it provides a reference to the SGML declaration, and to HyTime processing instructions in the case HyTime is being used.
The SGML_STRING will be used in the definition of standard STEP APs (application protocols) and will thus be automatically configured as part of the products defined by these standards.
During the design, production, etc. phases of the product life-cycle the designers, engineers, technical writers, etc. will add documentation, in the form of SGML_STRINGs, to the appropriate components of the product.
During the phases of the life-cycle where documentation is produced, for example where the product is instantiated from the database, the documentation will also be instantiated together with the appropriate STEP data (transformed into character codes). The instantiated documentation file can be exported (see step 4 in the Architecture diagram below) to an SGML environment where it can be published, parallel to the production of the actual product.
An example of how document modelling might be achieved in STEP is shown in the diagram below, using EXPRESS-G;
