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Re: Digging through section 6.2.1 / multiple types for an element

From: Lars Oppermann <Lars.Oppermann@Sun.COM>
Date: Thu, 06 Apr 2006 17:54:10 +0200
To: John Boyer <boyerj@ca.ibm.com>
Cc: Allan Beaufour <beaufour@gmail.com>, "Nick_Van_den_Bleeken@inventivedesigners.com" <Nick_Van_den_Bleeken@inventivedesigners.com>, www-forms@w3.org, www-forms-request@w3.org
Message-id: <443539A2.1050104@sun.com>

Hi John,

John Boyer wrote:
> I especially don't see where it says that type MIP "is like xsi:type"
>  thereby implying some effect of the type MIP on the PSVI.  This is
> especially true because XForms does not strictly require a
> PSVI-capable schema processor, nor does it require a host language to
>  even have a CSS processor such that hypothetical effects of the type
> MIP on the non-required PSVI could be operated on by the non-required
> CSS selector.


Well, it does say, that it is like xsi:type in 6.1.1, but it doesn't
draw the conclusion, that this has any effect on the PSVI.

My thoughts on some hypothetical PSVI based CSS selector don't add
anything useful to this particular discussion. So lets leave those aside.

Regarding xsi:type and the type-MIP, I think the fact that the type-MIP
is something layered on top of anything that goes on in 'schema-land' is
clear from the spec. What I still find confusing (I am also no master in
XSD questions) is that XSD-1
(http://www.w3.org/TR/xmlschema-1/#xsi_type) introduces xsi:type as a
way of explicitly assigning a schema type to an element. XSD-1 is also
laying out rules that if an information item has an xsi:type, as well as
a schema type, the xsi:type must be derived from the expected schema type.

By saying, the type-MIP behaves like xsi:type, one might argue, that
XForms is implying the XSD handling of xsi:type.

Maybe it would be clearer, if it says, that in the XForms model,
xsi:type attributes on elements should behave like a type-MIP of that
type being applied to that element, rather than the other way round.
That way, an implementation that is not supporting schema validation
could still use the xsi:type information by generating type-MIPs from
them, as in XForms Basic.

In 6.2.1 (Atomic Datatype) the XForms spec gives three sources for XML
Schema facets, the first being "An XML Schema associated with the
instance data" and than "An XML Schema xsi:type attribute in the
instance data".
But with what I quoted from XSD-1 above, the xsi:type facet would
already have been applied by the schema validation according to the
rules given in XSD-1 (derivation requirement &c)

So now, to me it looks like xsi:type has two possibly conflicting
meanings in XForms and XSD:
- In xsd, xsi:type must not conflict with the schema type
- In XForms the type-MIP can very well conflict with the schema type,
authors are discouraged to do so, but they may if they choose to do so.
- _but_ XForms also says type-MIP is to behave like xsi:type

This conflict was also the main issue in Leigh's mail:
http://lists.w3.org/Archives/Public/www-forms-editor/2004Aug/0003
with regards to the handling in Basic vs. Full.



/lars




-- 
Lars Oppermann <lars.oppermann@sun.com>               Sun Microsystems
Software Engineer - StarOffice                           Sachsenfeld 4
Phone: +49 40 23646 959                                D-20097 Hamburg
Fax:   +49 40 23646 550                  http://www.sun.com/staroffice
Received on Thursday, 6 April 2006 15:54:19 GMT

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