Accepting non-deterministic content models

["Roger L. Costello" <costello@mitre.org>]

Hi Folks,

The following element, test, has a non-deterministic content model:

<xsd:element name="test">
    <xsd:complexType>
        <xsd:choice>
            <xsd:element name="a" type="xsd:string"/>
            <xsd:element name="b" type="xsd:string"/>
            <xsd:sequence>
               <xsd:element name="a" type="xsd:string"/>
               <xsd:element name="b" type="xsd:string"/> 
            </xsd:sequence>
        </xsd:choice>
    </xsd:complexType>
</xsd:element>

XML Spy 4.0b, xerces 1.4.1 both accept this as valid.

xsv, turbo XML 2.2, and the IBM SQL all generate an error, indicating
that the element, test, has a non-deterministic content model.

Isn't this a bad thing - some parsers accepting non-deterministic
content models, while other parsers rejecting it?

I believe that the origin of this "problem" is that in the XML spec it
states that parsers *should* reject non-deterministic content models.  I
am wondering if perhaps "should" would be better replaced with "must"? 
/Roger