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Re: Question on xsd:import

From: Roberto Chinnici <Roberto.Chinnici@Sun.COM>
Date: Tue, 16 Sep 2003 14:19:12 -0700
To: "Amelia A. Lewis" <alewis@tibco.com>
Cc: mgudgin@microsoft.com, www-ws-desc@w3.org
Message-id: <3F677E50.9050008@sun.com>

Amelia A. Lewis wrote:
> On Tue, 16 Sep 2003 09:59:11 -0700
> Roberto Chinnici <Roberto.Chinnici@Sun.COM> wrote:
> 
>>Amelia A. Lewis wrote:
>>
>>>On Tue, 16 Sep 2003 03:11:09 -0700
>>>Martin Gudgin <mgudgin@microsoft.com> wrote:
>>>
>>>
>>>>This text first appeared in wsdl12.xml CVS revision 1.34.2.2 as part
>>>>of the types work ( it was subsequently merged into the main branch
>>>
>>>in>version 1.35 ). It was part of the write up that Amy did, I think.
>>>
>>>>Note that this ONLY applies to schemas that DO NOT have a target
>>>>namespace. It cannot be used to override the namespace of an
>>>
>>>imported>schema document that DOES have a target namespace. The text
>>>
>>>>essentially means that all schemas constructs are qualified. I can't
>>>>remember the rationale for allowing this, perhaps Amy will have
>>>
>>>better>powers of recall.
>>>
>>>
>>>As I recall, this deals with XML Schemas that were originally
>>>designed for use as "chameleons", and it also provides a pattern for
>>>use with other schema languages (for instance, the DTD example uses
>>>a similar technique to place all of the elements imported into a
>>>single namespace).
>>
>>Yes, but the dtd:import element is brand new, so we can assign it an
>>arbitrary semantics. It worries me that we're redefining how the
>>xsd:import construct works. This new functionality doesn't seem to
>>be too well defined either.
>>
>>For instance, wouldn't the clause "as if it contained a corresponding
>>targetNamespace declaration" be likely to break the references between
>>components in the imported schema? After all, if I did literally what
>>the spec says, i.e. read the schema in, ran a transform on it to set
>>its targetNamespace attribute to the desired value, then processed the
>>resulting document per the XML Schema spec, I'd most likely run into
>>some invalid references.
> 
> 
> Entirely possible, with a complex schema.  Solution is to namespace the
> schema internally.  If it isn't editable, and doesn't have a namespace,
> and breaks when a namespace is imposed, it's not usable.
> 
> 
>>By the way, I'm not sure what you mean by "chameleons". Could you
>>clarify that?
> 
> 
> No.  Google for it; it's a sufficiently complex topic that we don't need
> to go into it here.

Done, thanks. The references I found tell me that these chameleons are
quite a hack, that there are indeed problems with references to 
components within them and mostly that you shouldn't use them. Given all
this, I see even less of a reason to invent a new xsd:import construct
just to accommodate them. The workaround of defining your own schema,
have it include the chameleon and then xsd:import it (or inline it)
in your WSDL seems entirely acceptable, and from my point of view is
preferable to having the WSDL spec step into XML Schema's territory.

Roberto


> Amy!
> 
>>Thanks,
>>Roberto
>>
>>
>>>As Gudge says, I believe that this is simply intended to force
>>>schemas lacking namespaces into a namespace.  The principle is
>>>simplicity: if you're going to refer to components of a schema by
>>>namespace, it ought to be the same as the namespace that labels the
>>>import.  But I believe the language was specifically chosen to avoid
>>>allowing chameleons.
>>
>> >
>>
>>>Amy!
>>>
>>>
>>>>I would note that this text was reviewed as part of the types work
>>>
>>>in>January 2003 and was agreed by the WG. That said, I don't feel
>>>
>>>>strongly about it and would be happy for us to open an issue to
>>>>claridy this point.
>>>>
>>>>Gudge
>>>>
>>>>
>>>>
>>>>>-----Original Message-----
>>>>>From: www-ws-desc-request@w3.org 
>>>>>[mailto:www-ws-desc-request@w3.org] On Behalf Of Roberto Chinnici
>>>>>Sent: 16 September 2003 01:06
>>>>>To: www-ws-desc@w3.org
>>>>>Subject: Question on xsd:import
>>>>>
>>>>>
>>>>>It's been about a year since we last talked about imports. In
>>>>>section 3.1.1.1 of part 1 of the spec I found this sentence 
>>>>>describing how xsd:import works (the text in square brackets is
>>>>>mine):
>>>>>
>>>>>"If the [imported] schema does not have a targetNamespace 
>>>>>AII, then the namespace specified by the namespace AII [of 
>>>>>the xsd:import EII inside the wsdl:type EII] is applied to 
>>>>>all components of the schema as if it contained a 
>>>>>corresponding targetNamespace declaration."
>>>>>
>>>>>This looks very different from what XML Schema does. It seems 
>>>>>that to honor this clause a WSDL processor would need to use 
>>>>>a specially rigged XML Schema processor that allows for this 
>>>>>namespace overriding to happen.
>>>>>
>>>>>Can someone refresh my memory as to when we approved the text 
>>>>>above and what its rationale was?
>>>>>
>>>>>Thanks,
>>>>>Roberto
>>>>>
>>>>>--
>>>>>Roberto Chinnici
>>>>>Java Web Services
>>>>>Sun Microsystems, Inc.
>>>>>roberto.chinnici@sun.com
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
> 
Received on Tuesday, 16 September 2003 17:17:55 GMT

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