What is a namespace ... really?

Fri Jan 15 14:54:28 GMT 1999

Roger L. Costello wrote:

> Suppose that I create a DTD (BookCatalogue.dtd).  In this DTD I define some
> elements, attributes, entities, etc.  I define the relationships between
> the elements, attributes, etc.  I place BookCatalogue.dtd in a directory:
> 
> file://localhost/xml-course/xml-part1/BookCatalogue.dtd
> 
> Is this a namespace?  That is, is the file itself (BookCatalogue.dtd) a
> namespace?

No, not as such.  To have a namespace, you must define attributes
*in the document* that have the form

	xmlns:prefix='some URI'

where "some URI" is intended to remain stable.

> In all the examples that I see in the namespace spec they don't refer to a
> specific file.  Instead, they refer to "some place", such as:
> 
> http://www.w3.org/TR/HTML/
> 
> So, perhaps the "directory" that BookCatalogue.dtd resides in is the
> namespace? i.e.,

It can be used as such if you decide to do so.  Or you can refer
to the DTD itself as the namespace name.  Or any URL you want;
the URL does not have to refer to anything in particular.

> file://localhost/xml-course/xml-part1/

This wouldn't be so useful, because it means different things on
different hosts.  But again, the URI is just used as a thing to
compare to determine if two namespaces are the same or different.

-- 
John Cowan	http://www.ccil.org/~cowan		cowan at ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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