XSchema Spec - XSchema Element (Sections 2.0 and 2.1), Draft 7

[Simon St.Laurent]

This reflects our latest thinking regarding namespaces and XSchema.

The main changes involve the removal of the Namespace element and its 
replacement with attributes in the XSchema element and also (to come) in 
element and attribute declarations.  

I'm hoping this will get us past the thorny namespace issues so that I can 
move on to the rest of the spec, compile a complete DTD and an updated 
complete version of the spec so far, and start work on sections 4 and 5 on 
processing.

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 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)*)>
<!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 
8/2/98 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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