Another look at namespaces

Simon St.Laurent simonstl at
Thu Sep 16 17:59:53 BST 1999

At 08:30 AM 9/16/99 -0700, Andrew Layman wrote:
>[Someone] wrote that, although a schema may be somehow associated with a
>namespace, the "meaning" of markup will be determined in a number of ways
>such as style sheets, or procedural code, or maybe the schema.  I believe
>this understates the importance of the schema.  A schema makes a
>contribution to the Infoset. It does this by providing default values and --
>under some recent proposals -- by indicating type information, which may be
>considered also a form of default value.  Elements defined by a schema, when
>used in an instance document in a validating processor, will have these
>default values available, and this fact is pertinent to the author of the
>document.  This means that an element is incompletely read if the schema for
>it is not read. 

With all due respect to Andrew Layman, I find this to be a gross
overvaluation of schemas, and a substantial contrast with both the XML 1.0
approach (which doesn't require validation) and with Tim Berners-Lee's
comments, which included:

>However, as we define languages for talking about languages
>(XML and RDF schemas for example, even style sheets)
>the document corresponding to the namespace URI becomes
>the place where the namespace-author can put *definitive*
>information about the intent of the namespace.

This seems to leave the possibility _wide_ open that something other than a
schema is lurking at the URI identified by the namespace.  At the very
least, there are multiple schema possibilities - XML and RDF, as noted
above, and possibly even DTDs.

Schema information should be an important _component_ of that information,
certainly, but I see no reason why it should be the only, or indeed
primary, component.  For an example of a different possibility, you might
explore my XPDL proposal at  Schema
information, style information, and documentation are combined to provide a
description of a document class.

>For a namespace to be reliably useful, there must be a document
>defining its contents and their meaning.  A schema is, for many namespaces,
>that document.

An interesting opinion, to be sure, but not a claim made directly by the
Namespaces in XML recommendation, and not necessarily a hard-and-fast rule.

Simon St.Laurent
XML: A Primer (2nd Ed - September)
Building XML Applications
Inside XML DTDs: Scientific and Technical
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