Because type is for datatype, there should not be a problem for XForms Basic

A datatype can come from a simple or complex type. It is defined in order 
to have vocabulary to talk about
the validation of character data, but the schema spec even talks about 
getting datatypes from derivations
and other such 'complex' mechanisms.

So, as long as the XForms type MIP is properly interpreted as only 
assigning a datatype (as Section 6.1.1
defines the type MIP), then XForms basic could be required to only support 
enough of schema to make
rudimentary type MIPs work.

The support of xsi:type could then follow the restriction down to what the 
type MIP is capable of.

When an unrecognized type is referenced, it defaults down to xsd:string, 
which matches pretty much everything.

This means that basic processors would sometimes submit data that 
shouldn't be submitted, which we 
already accept.  It also means that basic processors would never reject a 
submission that should be valid.

On the other hand, if unrecognized types are defaulted to xsd:string, and 
the basic processor did try to support
xsi:type and the type MIP for things that are not datatypes, then there 
would be structural validations that
would fail on an xforms basic processor when they shouldn't. 

I believe this is the part that's undesirable, so it makes sense to stick 
to the definition of the XForms type MIP, 
then apply that to the processing of xsi:type that might be expected of a 
basic processor (if any).  I admit that 
I've been leaving the details of basic to the implementers, but I had 
rather thought that Basic would support 
*only* the xforms type mip on the predefined datatypes, and that it would 
just ignore xsi:type and XML schema 
declarations altogether.  If that has any basis in fact, then again we 
don't have a problem for basic as long
as the type MIP is interpreted as datatype only.

Cheers,
John M. Boyer, Ph.D.
Senior Product Architect/Research Scientist
Co-Chair, W3C XForms Working Group
Workplace, Portal and Collaboration Software
IBM Victoria Software Lab
E-Mail: boyerj@ca.ibm.com  http://www.ibm.com/software/

Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer