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   RE: XML Schemas: Best Practices

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  • From: "Arnold, Curt" <Curt.Arnold@hyprotech.com>
  • To: "'xml-dev@lists.xml.org'" <xml-dev@lists.xml.org>
  • Date: Fri, 22 Sep 2000 12:18:04 -0600

Namespaces should be explicit, at least, when each namespace is describes a different domain.  For example, if I build a camera namespace and need to have hypertext embedded at certain locations, the
best approach is to import the standard XHTML namespace and use qualified XHTML elements for example <xhtml:p> for paragraph.  This allows existing XHTML processing code to work on the embedded XHTML.

If a distinct, but semantically similar "Camera Hypertext Markup Language" was created, existing XHTML processing code would have to be modified to recognize <camera:p> as being identical in semantics
to <xhtml:p>.

The example you contrived has multiple namespaces that cover at closely related information, hence the impetus to unify these in the instance document vs in the schema.

A much better design would be for the camera namespace to declare the framework for the document and individual vendor namespaces to be used for vendor-specific information.  For example:

<camera xmlns="http://www.example.com/camera">
		<fubar:lens xmlns:fubar="http://www.fubar.com/camera" partNo="fb10204" inspector="#3454"/>
		<zeon:body xmlns:zeon="http://www.zeon.com/camera" material="titanium"/>

The camera namespace can be declare to allow elements from outside namespaces using the <xsd:any> particle or equiv classes could be used (for example, fubar:lens could be in the camera:vendorLens
equiv class).


[Interestingly, for the video-game schema I don't
see how to make geometry, lighting, and voice global.  Any thoughts?]

They are only global (and only accessible from other namespaces) if they appear at the top level in the imported schemas.


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