DATEX schema converter as several issues

[nmco]

Several issues where found with the GML schema generated by the automatic tool, the most relevant ones are:

• [ ] repeated names for simple types
• [ ] properties of the super types are not taken into account
• [ ] properties of the extensions are not take into account

[nmco]

MultilingualString XML structure is not correctly handled:

<xs:complexType name="MultilingualString">
  <xs:sequence>
    <xs:element name="values">
      <xs:complexType>
        <xs:sequence>
          <xs:element maxOccurs="unbounded" name="value" type="D2LogicalModel:MultilingualStringValue"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
  </xs:sequence>
</xs:complexType>
<xs:complexType name="MultilingualStringValue">
  <xs:simpleContent>
    <xs:extension base="D2LogicalModel:MultilingualStringValueType">
      <xs:attribute name="lang" type="xs:language"/>
    </xs:extension>
  </xs:simpleContent>
</xs:complexType>
<xs:simpleType name="MultilingualStringValueType">
  <xs:restriction base="xs:string">
    <xs:maxLength value="1024"/>
  </xs:restriction>
</xs:simpleType>