Element-Mandatory Attribute declaration in XSD Schema:

Question

I want to declare an element to be included in a complex type declaration, and the element has a mandatory attribute: "option=MyOption", but the value of the "option" attribute could be anything, depending on the context.

That is: the attribute "option" with some unknown value should be mandatory in any document using the complex type containing this element.

Example:

    <xs:element name="SpecialOption" type="xs:string"/>

    <xs:complexType name="SpecialOptions">
        <xs:sequence>
            <xs:element ref="SpecialOption" minOccurs="1" maxOccurs="100"/>
            <xs:element ref="XXX"/>     
        </xs:sequence>
    </xs:complexType>   

In this case the "SpecialOption" element in the complex type "SpecialOptions" should have this mandatory attribute.

I don't know how to declare a mandatory attribute for an element in XSD, or how to specify that the attribute must have a value that is not yet known.

Answer 1

You need to modify the definition of the "SpecialOption" element to include the required attribute. Update this code:

<xs:element name="SpecialOption" type="xs:string"/>

to this:

<xs:element name="SpecialOption">
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:string">
        <xs:attribute name="Option" type="xs:string" use="required"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

With this change your complex type will contain the required "Option" attribute on all instances of the "SpecialOption" element in the "SpecialOptions" complex type. Declaring the "Option" attribute to be of type xs:string will allow any value to be passed in this field.

Answer 2

1) This is a simple required string attribute

<xs:element name="SpecialOption">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="Option" type="xs:string" use="required"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element> 

2) To require exactly one of a list of allowed values:

<xs:element name="SpecialOption">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="Option" use="required">
                    <xs:simpleType>  
                        <xs:restriction base="xs:string">  
                            <xs:enumeration value="DE"/>  
                            <xs:enumeration value="EN"/>  
                        </xs:restriction>  
                    </xs:simpleType>  
                </xs:attribute>  
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element> 

3) One can use a range as a restriction, like in the example below.

<xs:element name="SpecialOption">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="Option" use="required">
                    <xs:simpleType>  
                        <xs:restriction base="xs:integer">  
                            <xs:minInclusive value="95"/>  
                            <xs:maxInclusive value="137"/>  
                        </xs:restriction>  
                    </xs:simpleType>  
                </xs:attribute>  
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element> 

4) Below, the attribute is declared as a list containing decimal values. This allows an attribute to contain a subset of the specified values, e.g. Option="6 77 95".

<xs:simpleType name="Items">  
    <xs:restriction base="xs:decimal">  
        <xs:enumeration value="137"/>  
        <xs:enumeration value="95"/>  
        <xs:enumeration value="6"/>  
        <xs:enumeration value="77"/>  
    </xs:restriction>  
</xs:simpleType>  
<xs:element name="SpecialOption">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="Option" use="required">
                    <xs:simpleType>  
                        <xs:list itemType="Items"/>  
                    </xs:simpleType>  
                </xs:attribute>  
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element> 

5) Here the attribute is declared optional, but provided with a default value ("test"), which is sometimes sufficient:

<xs:element name="SpecialOption">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="Option" type="xs:string" use="optional" default="test"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element>