Re: Xerces developers - there's a bug in Xerces schema validation

Yes, this is one of the rare occasions on which I made a conscious decision to depart from the specification and get it right where the spec got it wrong.

Michael Kay
Saxonica


> On 25 Feb 2016, at 18:15, George Bina <george@oxygenxml.com> wrote:
> 
> Well, in general Xerces is right, according with the 1.0 spec, which defines the algorithm as a normative reference.
> 
> Basically, according to 2.1 of
> https://www.w3.org/TR/xmlschema-1/#cos-particle-restrict
> Any top-level element declaration particle (in R or B) which is the {substitution group affiliation} of one or more other element declarations and whose ·substitution group· contains at least one element declaration other than itself is treated as if it were a choice group whose {min occurs} and {max occurs} are those of the particle, and whose {particles} consists of one particle with {min occurs} and {max occurs} of 1 for each of the declarations in its ·substitution group·.
> 
> the algorithm will try to align
> 
>            <xs:choice minOccurs="0" maxOccurs="unbounded">
>                <xs:element ref="A" minOccurs="1" maxOccurs="1"/>
>                <xs:element ref="B" minOccurs="1" maxOccurs="1"/>
>            </xs:choice>
> 
> as base, against
> 
>            <xs:element ref="B" minOccurs="0" />
> 
> as derived.
> 
> Having an element in the derived and a choice in the base will get us to follow the rule
> https://www.w3.org/TR/xmlschema-1/#rcase-RecurseAsIfGroup
> 
> which will check
> 
>            <xs:choice minOccurs="0" maxOccurs="unbounded">
>                <xs:element ref="A" minOccurs="1" maxOccurs="1"/>
>                <xs:element ref="B" minOccurs="1" maxOccurs="1"/>
>            </xs:choice>
> as base, against
>            <xs:choice minOccurs="1" maxOccurs="1">
>                <xs:element ref="B" minOccurs="0" />
>            </xs:choice>
> as derived, according to
> ***
> For an element declaration particle to be a ·valid restriction· of a group particle (all, choice or sequence) a group particle of the variety corresponding to B's, with {min occurs} and {max occurs} of 1 and with {particles} consisting of a single particle the same as the element declaration must be a ·valid restriction· of the group as defined by Particle Derivation OK, (All:All,Sequence:Sequence -- Recurse) (§3.9.6), Particle Derivation OK (Choice:Choice -- RecurseLax) (§3.9.6) or Particle Derivation OK (All:All,Sequence:Sequence -- Recurse) (§3.9.6), depending on whether the group is all, choice or sequence.
> ***
> 
> Which will get us to
> https://www.w3.org/TR/xmlschema-1/#rcase-RecurseLax
> where the occurrence range is ok, but we need to check
> ***
> 2 There is a complete ·order-preserving· functional mapping from the particles in the {particles} of R to the particles in the {particles} of B such that each particle in the {particles} of R is a ·valid restriction· of the particle in the {particles} of B it maps to as defined by Particle Valid (Restriction) (§3.9.6).
> ***
> 
> for
>                <xs:element ref="A" minOccurs="1" maxOccurs="1"/>
>                <xs:element ref="B" minOccurs="1" maxOccurs="1"/>
> 
> against the derived
> 
>                <xs:element ref="B" minOccurs="0" />
> 
> and we cannot find that as the range check of the reference to B in the base type will not include the range specified in the reference to B in the derived type.
> 
> So, it looks like Xerces is right to report an error and it points exactly to point 2 from the above rule
> https://www.w3.org/TR/xmlschema-1/#rcase-RecurseLax
> 
> but of course that is not intuitive, but it is the conformant behavior according to the 1.0 spec.
> 
> You can see also now that if you put minOccurs="1" on B in the derived type:
> 
> <xs:element ref="B" minOccurs="1" />
> 
> then that will match against the (1:1) occurrence in the base and that is why you do not get an error in that case.
> 
> Hope this helps!
> 
> Best Regards,
> George
> --
> George Cristian Bina
> <oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
> http://www.oxygenxml.com
> 
> On 25/02/16 19:01, Costello, Roger L. wrote:
>> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
>> xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"  vc:minVersion="1.1">
>> 
>>      <xs:element name="A" type="xs:double" />
>>      <xs:element name="B" substitutionGroup="A" type="xs:double" />
>> 
>>      <xs:complexType name="base">
>>          <xs:sequence>
>>              <xs:element ref="A" minOccurs="0" maxOccurs="unbounded" />
>>          </xs:sequence>
>>      </xs:complexType>
>> 
>>      <xs:complexType name="derived">
>>          <xs:complexContent>
>>              <xs:restriction base="base">
>>                  <xs:sequence>
>>                      <xs:element ref="B" minOccurs="0" />
>>                  </xs:sequence>
>>              </xs:restriction>
>>          </xs:complexContent>
>>      </xs:complexType>
>> </xs:schema>
>

Received on Thursday, 25 February 2016 18:44:09 UTC