Rationale for restricted uses of "all"

Just curious: what are the rationale for the particular constraints on the
use of "all"? Is it that parsing becomes intractable, or are there other
issues?

		Schema Component Constraint: All Group Limited 
		When a model group has {compositor} all all of the following
must be true: 
		1 one of the following must be true: 
		1.1 It appears as the model group of a model group
definition. 
		1.2 It appears in a particle with {min occurs}={max
occurs}=1, and that particle must be part of a pair which constitutes the
{content type} of a complex type definition. 
		2 The {max occurs} of all the particles in the {particles}
of the group must be 0 or 1. 


Also, the constraints also restrict the ability to combine all groups
through "inheritance?" Say a base type has an all group and an extension of
that type also defines an all group:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">
     <xs:complexType name="A">
          <xs:all>
               <xs:element name="Child1"/>
          </xs:all>
     </xs:complexType>
     <xs:complexType name="B">
          <xs:complexContent>
               <xs:extension base="A">
                    <xs:all>
                         <xs:element name="Child2"/>
                    </xs:all>
               </xs:extension>
          </xs:complexContent>
     </xs:complexType>
     <xs:element name="ElementA" type="B"/>
</xs:schema>

Could they be interpreted as a single, combined all group?

<ElementA xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="allAgain.xsd">
   <Child1/>
   <Child2/>
</ElementA>

At present, Xerces reports

		[Error] allAgain.xml:3:138: schema error:
cos-all-limited.1.2:  An "all" model group that is part of a complex type
definition must constitute the entire {content type} of the definition. 

XML Spy And XSV report no errors.





----------------------------------------------------------------------------
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Mark Feblowitz                                   [t] 617.715.7231
Frictionless Commerce Incorporated     [f] 617.495.0188 
XML Architect                                     [e]
mfeblowitz@frictionless.com
400 Technology Square, 9th Floor 
Cambridge, MA 02139 
www.frictionless.com

Received on Thursday, 8 November 2001 14:00:37 UTC