RE: [xml-dev] The purpose of a namespace URI is ...

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

At 2012-11-30 16:40 +0000, Costello, Roger L. wrote:
>Hello David,
>
> > The local part in that case is not referring to markup or an XML
> > vocabulary at all, it is just the identifier of an error, the identifier
> > is almost never used in XML markup.
>
>So,
>
>     {http://www.w3.org/2005/xqt-errors} FOER0001
>     {http://www.w3.org/2005/xqt-errors} FOER0002
>     {http://www.w3.org/2005/xqt-errors} FOER0003
>     ...
>
>is not an XML vocabulary but,
>
>     {http://www.bookstore.org}BookStore
>     {http://www.bookstore.org}Book
>     {http://www.bookstore.org}Author
>     ...
>
>is an XML vocabulary?
>
>Why?

Because an XML vocabulary is a set of elements and attributes whose 
names can be qualified by namespace URI strings to distinguish them 
from other elements and attributes.  The error codes is a set of 
values qualified by namespace URI strings to distinguish them from 
other error codes created by the user.

>What distinguishes them that allows me to know this?

The context of how the URI strings are used, not anything in the URI itself.

The qualified name "{http://saxon.sf.net/}eval"; is used to identify 
an extension function, not an element, nor an attribute, nor an error code.

>So the first set of xs:QNames is not an XML vocabulary but the 
>second set of xs:QNames is an XML vocabulary?

No, any set of xs:QNames is a set of qualified names that, when used 
properly, uniquely distinguish and may even identify what is being 
named from other things that are also named.

>Why?
>
>I thought that -- by definition -- an XML vocabulary is a set of 
>xs:QNames, where each local part has the same namespace URI part.
>
>No?

Not as I see it.  An XML vocabulary is a set of element and attribute 
names that may be qualified with namespace URI strings.  In addition 
the vocabulary may have one of many valid structures (one or more 
document models (schemas/DTDs), perhaps many to cover the life cycle 
of a document) and perhaps business rules that cannot be expressed as 
schema constraints.

I understand the naissance of qualified names using namespace strings 
was for elements and attributes.  But as I said in an earlier post 
because of their properties they have long been used for many things 
such as XSLT extension function identifiers, which have nothing to do 
with elements and attributes.  The recent application of namespace 
strings to identify error codes is just yet another application of 
qualified names to take advantage of those properties.  But that 
doesn't make the error codes "an XML vocabulary".

It is just a naming convention with important properties of 
distinction and possibly identification.

. . . . . . . Ken

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