XSchema Spec - XSchema Element (Sections 2.0 and 2.1), Draft 9

[Simon St.Laurent]

Now that we have a content model container element, it makes sense to use
it to
contain the random parts that were clustering in the XSchema element.
Hence, a
revised and simplified XSchema element.  Hopefully, this is the _last_
revision
of this section.

As always, a prettier HTML version of this will be posted shortly at
http://purl.oclc.org/NET/xschema.

Simon St.Laurent
Dynamic HTML: A Primer / XML: A Primer / Cookies 

2.0 XSchema Syntax

This section describes XSchema document syntax. In version 1.0, 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. In future versions of XSchema, XSchema
elements may be embedded in instance documents.

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 | Model | AttDef | AttGroup |
Notation | XSchema)*)>
<!ATTLIST XSchema
xmlns CDATA #FIXED "http://www.purl.org/NET/XSchema/v1"
xmlns:XSC CDATA #FIXED "http://www.purl.org/NET/XSchema/v1"
prefix NMTOKEN #IMPLIED
ns CDATA #IMPLIED
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.


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