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Re: import vs prefixing

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 17 Jan 2001 15:08:02 +0000
To: Michael Anderson <michael@research.canon.com.au>
Cc: "xmlschema-dev@w3.org" <xmlschema-dev@w3.org>
Message-ID: <f5b4ryykyi5.fsf@cogsci.ed.ac.uk>
Michael Anderson <michael@research.canon.com.au> writes:

> I'm curious to know the difference between the two following schemas
> <schema xmlns="http://www.w3.org/2000/XMLSchema"
>               xmlns:cisra = "http://cisra.au">
>   <import namespace="http://cisra.au"
>                schemaLocation="http://www.cisra.com.au/mySchema.xsd"/>
>     <element name="food" type="cisra:Weetbix"/>
> </schema>
> <schema xmlns="http://www.w3.org/2000/XMLSchema"
>               xmlns:cisra = "http://cisra.au">
>               xsi:schemaLocation="http://cisra.au
> http://www.cisra.com.au/mySchema.xsd"/>
>     <element name="food" type="cisra:Weetbix"/>
> </schema>

[Note your NS URI for XML Schema is in error, should be

> Is it that you _must_ import the namespace using <import> before you can
> use components from it in your schema?

Yes.  And the imported schema must have "http://cisra.au" as its

> Also, while on the subject of import....
> There is also a statement in the specs [Structures 6.2.3] - "When a
> schemaLocation is present, it must contain a single URI reference which
> the schema author warrants will resolve to a schema document containing
> the component(s) in the imported namespace referred to elsewhere in the
> containing schema document."  This sounds to me like a constraint
> (although it doesn't appear in the src) that components referred to
> elsewhere in the containing document _must_ come from this schema
> document.  I'm pretty sure this is not the case as schemaLocation is,
> elsewhere, _always_ used as a _hint_only_.  In which case, is this
> statement saying that the schema document, if resolved, _must_ have at
> least one component that is in a schema information item that has a
> targetNamespace that matches the import statement?

No, and I'll try to change the prose to be less misleading in this

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Wednesday, 17 January 2001 10:08:06 UTC

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