2.0 XSchema Syntax

This section describes the XSchema document syntax. The XSchema document is an XML document containing a single XSchema element in which information describing the schema is nested. The XSchema element must be preceded by an XML declaration and may be preceded by other declarations, comments, and processing instructions.

2.1 The XSchema Element

The XSchema element is the root element for all XSchema documents. The declaration for the XSchema element is:

<!ELEMENT XSchema (Doc?, More?, (ElementDecl | AttDef | Model | Choice | Sequence | Mixed | Ref | Notation | XSchema)*)>

    xmlns CDATA #FIXED "http://www.purl.org/NET/XSchema/v1"
    xmlns:XSC CDATA #FIXED "http://www.purl.org/NET/XSchema/v1"
    Version CDATA #FIXED "1.0"
    MimeType CDATA "application/xml"
    FileExtension CDATA "xml"
    id ID #IMPLIED>

The XSchema element contains other elements describing the XSchema and building a schema. These elements are described in later sections of this specification. The XSchema element may also contain other XSchema elements nested inside of it. This nesting of XSchema elements improves reusability of XSchemas by allowing the combination of multiple XSchemas inside of a single XSchema framework. It also allows finer-grained control over documentation for subsections of an XSchema.

The XSchema element's attributes include information about the namespace used by XSchema, the version of the XSchema specification used, and information about the type of documents described by the XSchema.

The XSchema namespace is fixed with the xmlns attribute to correspond to the 2 August 1998 working draft of Namespaces in XML. The xmlns:XSC attribute, also fixed, allows XSchema declarations to be prefixed with XSC for situations where they need to redefine the default namespace (as is the case with XSC:Doc, and may be the case with XSC:More - see Section 2.6 for more details.) The prefix attribute identifies the prefix that will be applied to all elements and attributes defined within this XSchema element during conversion to DTDs, unless overridden in the element or attribute declaration itself. The ns attribute identifies the URI which functions as the namespace name for subelements. Namespace processing is covered further in Section 3.0, "XSchema and Namespaces".

Information about the XSchema specification version used to create this XSchema, contained in the Version attribute, is critical to proper handling of documents should the specification be updated in the future. This specification is identified as version 1.0. Future major and minor versions of the XSchema specification should identify themselves differently. No provision is made at this time for nesting XSchemas using different versions of the specification under a parent XSchema element.

The MimeType and FileExtension attributes are used to provide a suggested MIME (Multipurpose Internet Mail Extensions) Content-type and file extension for documents created using a particular XSchema. Applications may use this information to identify XML document types. A document library that generates XML documents dynamically could assign file extensions and MIME types based on the XSchema used.

Applications using this information should use the values stored in the first XSchema encountered during processing. For instance, if an XSchema includes another nested XSchema, the values for the MimeType and FileExtension attributes of the root XSchema should be used.

By default, most XML documents are assumed to have a MIME type of application/xml, as described in RFC 2376, "XML Media Types," by E.J. Whitehead and Murata Makoto. Developers who need different MIME types for documents created using particular XSchemas may register other MIME types with the IETF, as described in RFC 1590, or use the 'x-' prefix syntax for subtypes, as described in RFC 1521.