RE: can an attribute prohibited by restriction be added back through a subsequent extension?

We will investigate it.
Thanks, Yan

	-----Original Message-----
	From: Eddie Robertsson [mailto:erobertsson@allette.com.au] 
	Sent: Tuesday, July 30, 2002 5:26 PM
	To: Priya Lakshminarayanan
	Cc: xmlschema-dev@w3.org; Yan Leshinsky
	Subject: Re: can an attribute prohibited by restriction be added
back through a subsequent extension?
	
	
	Hi,
	
	This has been in my inbox now for quite some time and I was
actually waiting for some of the experts on the list to make a comment
on this. Maybe you have received a private answer but since I'm
interested in this as well I thought I'd give it ago.
	
	Priya Lakshminarayanan wrote:
	

		Is the following derivation sequence valid??

		 

		<xs:complexType name="CT">

		                        <xs:attribute name="x"
type="xs:int"/>

		                        <xs:attribute name="y"
type="xs:int"/>

		</xs:complexType>

		                

		 <xs:complexType name="CT2">

		                  <xs:complexContent>

		                        <xs:restriction base="CT">

		                          <xs:attribute name="x"
type="xs:int" use="prohibited"/>

		                        </xs:restriction>

		                  </xs:complexContent>

		 </xs:complexType>

		 

		  <xs:complexType name="CT3">

		                  <xs:complexContent>

		                        <xs:extension base="CT2">

		                          <xs:attribute name="x"
type="xs:int"/>

		                        </xs:extension>

		                  </xs:complexContent>

		  </xs:complexType>

		 

		I specifically need clarification on the following part
of the spec:

		Schema Component Constraint: Derivation Valid
(Extension)

		    1.5 It must in principle be possible to derive the
complex type definition in two steps, the first an extension and the
second a restriction (possibly vacuous), from that type definition among
its ancestors whose {base type definition}
<http://www.w3.org/TR/xmlschema-1/#ct-base_type_definition#ct-base_type_
definition>  is the *ur-type definition*
<http://www.w3.org/TR/xmlschema-1/#ur-type-itself#ur-type-itself> . 

		    

		NOTE: This requirement ensures that nothing removed by a
restriction is subsequently added back by an extension. It is trivial to
check if the extension in question is the only extension in its
derivation, or if there are no restrictions bar the first from the
*ur-type definition*
<http://www.w3.org/TR/xmlschema-1/#ur-type-itself#ur-type-itself> .

	Based on the above sentence I would say that the above example
is not legal since the type CT3 tries to add back an attribute that was
prohibited in a previous derivation step.
	

		

		 Constructing the intermediate type definition to check
this constraint is straightforward: simply re-order the derivation to
put all the extension steps first, then collapse them into a single
extension. If the resulting definition can be the basis for a valid
restriction to the desired definition, the constraint is satisfied.

	I've also tried to apply this rule to the above example and if
I'm doing that correctly then the example is invalid. To test the above
you should reorder the derivation steps so that all extensions come
first. The base type is:
	
	

	<xs:complexType name="CT">

	    <xs:attribute name="x" type="xs:int"/>

	    <xs:attribute name="y" type="xs:int"/>

	</xs:complexType>


	Now we reorder the derivation steps so that the next step will
be the extension which would be something like this:
	
	<xs:complexType name="test"> 

	    <xs:complexContent>

	        <xs:extension base="CT1">

	            <xs:attribute name="x" type="xs:int"/>

	        </xs:extension>

	    </xs:complexContent>

	</xs:complexType>

	
	Now, I think the above is illegal since you try to add the
attribute x to a type that already have an attribute x but I couldn't
find where this was specified in the rec. If I'm correct and the above
is indeed illegal then the test would fail and hence the above example
would be invalid. I decided to test this with a couple of W3C XML Schema
validators and got the following results:
	

	
	Invalid - XML Spy 4.4 
	
	

	Valid - XSV, SQC, Xerces (2.0.1), MSXML4
	

	
	I was very surprised at this result so I guess I missed
something in my above conclusion. 
	

	Can anyone comment on this?
	

	Cheers,
	/Eddie