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XML-L  January 2002

XML-L January 2002

Subject:

Re: a simple question about namespace

From:

"CHIUSANO, Joseph" <[log in to unmask]>

Reply-To:

General discussion of Extensible Markup Language <[log in to unmask]>

Date:

Fri, 18 Jan 2002 08:17:10 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (123 lines)

An additional point regarding instance documents:

To allow for validation of an XML instance document against a schema, you
can include the location of the schema and its associated targetNamespace at
the top of the instance document as follows:

        <?xml version="1.0"?>
        <Invoice xmlns:xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://www.acme.org/invoices"
                                                          InvoiceV1.xsd>

where xsi:schemaLocation indicates the targetNamespace of the schema whose
name is given in the second parameter.  This indicates that the schema named
InvoiceV1.xsd (assumed here to be in the same directory as the instance
document, which may not always be the case) has a targetNamespace of
"http://www.acme.org/invoices".  

For more information on targetNamespace (and namespaces in general), you can
reference chapter 3 of the W3C Schema Primer:
http://www.w3.org/TR/2000/CR-xmlschema-0-20001024/

Hope this helps,
Joe Chiusano

> **************************************************************************
>   Joseph M. Chiusano
>   Logistics Management Institute
>   2000 Corporate Ridge
>   McLean, VA 22102
>   Email: [log in to unmask]
>   Tel: 571.633.7722
> **************************************************************************
> 


-----Original Message-----
From: Ronald Bourret [mailto:[log in to unmask]]
Sent: Friday, January 18, 2002 3:38 AM
To: [log in to unmask]
Subject: Re: a simple question about namespace


Ying Su wrote:
>
> Hi all,
>
> As a beginner to XML, I have a question about the XML namespace.
> When I read those articles about this issue, I got to know that the
> namespaces are just identifiers, and they  are not guaranteed to
> point to anything.

Correct.

> I'm a little confused with that. Does it mean I can declare a
> namespace using a URI that does not exist at all?

Yes.

> For example is it correct to write like this:
> <text xmlns="http://www.doesNotExist.com/">  ?

No.

There is nothing to stop you from doing this. However, you should only
use URIs that are under your control. For example, there is no software
that will stop me from declaring the following namespace URI:

   <text xmlns="http://www.microsoft.com/rpbourret">

However, I should not do this because I do not own the microsoft.com
domain. Similarly, if you do not own the doesNotExist.com domain, you
should not use it.

> I wrote a simple xml file as follow:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <text xmlns="http://www.doesNotExist.com/">
>  <hehe>miao...</hehe>
> </text>
> When I try to validate it using XML SPY 4.1, I got the following
> error: "Unable to locate a reference to a supported  schema kind(DTD,
> DCD, W3C Schema, XML-data, Biztalk) within this document instance".
> Then it seems a namespace must be assosiated with some certain
> schema.

I do not know what is happening here. However, I don't think it has
anything to do with namespaces. It appears that XML Spy requires you to
use a schema. That is, it cannot edit schema-less documents. (This is
very surprising. Is it true?)

> I got confused. In my point of view, some XML namespace URIs were
> predefined, such as    xmlns:xs="http://www.w3.org/2001/XMLSchema" .
> They should be associated with some .xsd or dtd files, for example
> XMLSchema.xsd.

In practice, most namespaces apply to sets of elements that do have a
schema of some kind. However, the namespaces recommendation does not
require this.

> So my question is: Is my above thought right? If I am right, then how
> to associate the .xsd file with the URL?

It is not correct. Namespaces do not require you to associate the .xsd
file with the namespaces URL.

-- Ron
>
> Thanks a lot!
>
> Ying Su
>
> ʹ263 http://freemail.x263.net
> welcome to enjoy 263 Freemail http://freemail.x263.net
> _____________________________________________________
>                 263_й˵ϼ԰
> Tel:010-64240315 Fax:010-64240295 ?1998-2001Ȩ
> 263   010-64262631  [log in to unmask]

--
Ronald Bourret
Programming, Writing, and Research
XML, Databases, and Schemas
http://www.rpbourret.com

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