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Re: [xml-dev] XSD elementFormDefault="unqualified" destroys the benefitsof namespace modularity
- From: George Cristian Bina <george@oxygenxml.com>
- To: "Costello, Roger L." <costello@mitre.org>
- Date: Wed, 28 Jan 2009 15:51:03 +0200
Hi Roger,
The first instance imply 4 schemas (you need a different schema for each
namespace). The second instance cannot be obtained by setting the
elementsFromDefault to unqualified in all these 4 schemas so I believe
all the outcome further is irrelevant having a false presumption. The
second instance can be the result of a single schema that has
elementFormDefault (or the form attribute on each local element) set to
unqualified but that is a totally different thing than having 4 schemas.
Best Regards,
George
--
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com
Costello, Roger L. wrote:
> Hi Folks,
>
> Recall that with XML Schemas you can specify that all elements in conforming instance documents must be namespace-qualified using:
>
> elementFormDefault="qualified"
>
> Or, you can specify that only top-level, global elements must be namespace-qualified using:
>
> elementFormDefault="unqualified"
>
> These can yield remarkably different instance documents.
>
>
> INSTANCE #1
>
> Here is an example of an instance where the schema specifies "qualified":
>
> <?xml version="1.0"?>
> <c:camera xmlns:c="http://www.camera.org";
> xmlns:nikon="http://www.nikon.com";
> xmlns:olympus="http://www.olympus.com";
> xmlns:pentax="http://www.pentax.com";>
> <c:body>
> <nikon:description>Ergonomically designed casing for easy
> handling</nikon:description>
> </c:body>
> <c:lens>
> <olympus:zoom>300mm</olympus:zoom>
> <olympus:f-stop>1.2</olympus:f-stop>
> </c:lens>
> <c:manual_adapter>
> <pentax:speed>1/10,000 sec to 100 sec</pentax:speed>
> </c:manual_adapter>
> </c:camera>
>
>
> INSTANCE #2
>
> Using the same schema, but specifying "unqualified," here is the instance:
>
> <?xml version="1.0"?>
> <c:camera xmlns:c="http://www.camera.org";>
> <body>
> <description>Ergonomically designed
> casing for easy handling
> </description>
> </body>
> <lens>
> <zoom>300mm</zoom>
> <f-stop>1.2</f-stop>
> </lens>
> <manual_adapter>
> <speed>1/10,000 sec to 100 sec</speed>
> </manual_adapter>
> </c:camera>
>
>
> BENEFITS OF NAMESPACES
>
> Namespaces modularize instance documents. They enable applications to perform module-specific processing.
>
>
> MODULES IN INSTANCE #1
>
> In instance #1 the namespaces modularize the document. The document can be readily partitioned into these five modules:
>
> -------------------------------------------
> <c:camera xmlns:c="http://www.camera.org";>
> <c:body>
> </c:body>
> <c:lens>
> </c:lens>
> <c:manual_adapter>
> </c:manual_adapter>
> </c:camera>
> -------------------------------------------
> <nikon:description xmlns:nikon="http://www.nikon.com";>
> Ergonomically designed casing for easy handling
> </nikon:description>
> -------------------------------------------
> <olympus:zoom xmlns:olympus="http://www.olympus.com";>
> 300mm
> </olympus:zoom>
> -------------------------------------------
> <olympus:f-stop xmlns:olympus="http://www.olympus.com";>
> 1.2
> </olympus:f-stop>
> -------------------------------------------
> <pentax:speed xmlns:pentax="http://www.pentax.com";>
> 1/10,000 sec to 100 sec
> </pentax:speed>
> -------------------------------------------
>
>
> MODULES IN INSTANCE #2
>
> In instance #2 there is one namespace module and three no-namespace modules:
>
> -------------------------------------------
> <c:camera xmlns:c="http://www.camera.org";>
> </c:camera>
> -------------------------------------------
> <body>
> <description>Ergonomically designed
> casing for easy handling
> </description>
> </body>
> -------------------------------------------
> <lens>
> <zoom>300mm</zoom>
> <f-stop>1.2</f-stop>
> </lens>
> -------------------------------------------
> <manual_adapter>
> <speed>1/10,000 sec to 100 sec</speed>
> </manual_adapter>
> -------------------------------------------
>
>
> PROBLEMS WITH INSTANCE #2
>
> The no-namespace modules are comprised of multiple XML vocabularies. For example, in the lens module the <lens> element comes from the camera schema, whereas the <zoom> and <f-stop> elements come from the olympus schema.
>
> An application written for the olympus schema would not be able to process the lens module for these two reasons:
>
> a. The elements are not associated with the olympus namespace. Consider how the olympus application would behave upon encountering the lens module: "Is that <zoom> element really the element I know about, or is it somebody else's zoom element?
>
> b. The olympus application knows nothing about the <lens> element.
>
>
> RECOMMENDATION
>
> Don't use elementFormDefault="unqualified" in your XML Schemas. It destroys the modularity benefits provided by namespaces.
>
>
> Do you agree with this recommendation?
>
> /Roger
>
>
>
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