Imported from previous forum
FIXML is comprehensive, there are optional fields for just about everything. One common thing that users like to do is to restrict the schema definitions for their application domain.
One problem with XML Schema 2001 is the way it handles restrictions. It is impossible to restrict a sequence containing one element with a sequence containing no elements. e.g. removing the Hop element from the BaseHeaderElements. The cos-particle-restrict rules combined with the definition of pointlessness are to blame.
XML Schema 1.1 has vastly improved the restriction and extensions mechanisms. Given that extension and restriction are important to the successful adoption of FIXML, is there any intention to migrate to the newer version?
An alternative is to make sure that all sequences of a single element in the FIXML schemas are replaced with a slightly more complex form containing a sequence element that doesn’t change the valid messages. Could this be considered? An example of such a change would be:
<xs:group name=“BaseHeaderElements”>
xs:sequence
<xs:element name=“Hop” type=“Hop_t” minOccurs=“0” maxOccurs=“unbounded”/>
xs:sequence/
</xs:sequence>
</xs:group>