Help defining a complexType in schema

Question

Hi
I am hoping someone can help me out. I have a number of attributes in an xml file which contain different structures based on whether it has a single of multiple value.
As an example, one of these elements refers to optical filters. If it is single valued, the xml will look like <filter>I</filter> while if it has multiple values, the xml looks like <filter>
  <value>I</value>
  <value>J</value>
  <value>K</value>
</filter>The closest I have been able to come up with in validation to handle this is<xsd:element name="filter" type="filterType"/>
<xsd:complexType name="filterType" mixed="true">
  <xsd:complexContent>
    <xsd:restriction base="xsd:anyType">
      <xsd:choice>
        <xsd:element name="value" type="FilterList"
                     minOccurs="0" maxOccurs="unbounded"/>
      </xsd:choice>
    </xsd:restriction>
  </xsd:complexContent>
</xsd:complexType>
<xsd:simpleType name="FilterList">
  <xsd:restriction base="xsd:string">
    <xsd:enumeration value="I"/>
    <xsd:enumeration value="J"/>
    <xsd:enumeration value="K"/>
  </xsd:restriction>
</xsd:simpleType>This will validate it fine is it is multi-valued, but because of the use of xsd:anyType it does not validate if it is single valued. I have tried making restriction in FilterType based on FilterList, but the validating parser says this is an error.
Any suggestions on how to improve this?

Answer 1

I do not know of a way to make the filter both a simpleType and complexType. In order for both of those to be valid you would have to have a schema that would define the filter as a simple and complex type. It would be much easier if a single valued filter could be valid like so:
<filter>
   <value>I</value>
</filter>because something like this may work ....
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="filter">
        <xs:complexType>
        <xs:sequence>
            <xs:element name="value" minOccurs="1" maxOccurs="3">
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:pattern value="[IJK]"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
        </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>or perhaps
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="filter">
        <xs:complexType>
        <xs:sequence>
            <xs:element name="value" minOccurs="1" maxOccurs="3">
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:enumeration value="I"/>
                        <xs:enumeration value="J"/>
                        <xs:enumeration value="K"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
        </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>but I am unable to find a way to make your example valid.