This is a brief introduction to the ISO 10303-28 standard and directions for its use in the context of PLCS (Product Life Cycle Support).

Part 28 of the ISO 10303 standard (STEP) describes an XML based format for file exchange.

Whereas the first edition of ISO10303-28 specified the structure of XML exchange documents using Document Type Definitions (DTDs), Edition 2 of ISO10303-28 (as used in PLCS) specifies exchange structures using XML Schema, and specifies the mapping of the EXPRESS data model to an XML Schema data model. XML schemas are increasingly used to validate XML documents and are slowly taking over from the DTD approach in many areas of XML application.

Part 28 configuration options and PLCS

ISO 10303-28 allows for the use of a number of different options when constructing an XML schema from an EXPRESS schema. PLCS has adopted the default options (requiring an empty configuration file) as specified in Clause 4.1.2 of ISO 10303-28:2007(E):

An XML document shall conform as a uos document if it satisfies all of the following conditions:

• The root element for the document is a uos element.
• The data set encoded in the uos element conforms as specified in ISO 10303-11 to a given EXPRESS schema, designated the governing schema for that data set.
• The XML infoset for the uos element is valid with respect to the XML schema that is derived from the governing EXPRESS schema as specified in Clause 6.

NOTE    In a uos document, the uos element is the one that corresponds to the default mapping of the governing schema, that is, the one corresponding to an empty configuration file.