XSD - unique values of two different attributes

Question

It is possible at schema level to enforce unique values of two attributes with different name?

<xs:complexType name="exampleType">
  <xs:attribute name="first" type="xs:integer" use="required"/>
  <xs:attribute name="second" type="xs:integer"/>
</xs:complexType>

If first is 1, second needs to be some other value.

EDIT: I am using xsd 1.0.

Answer 1

As I said in my comment this is only valid if first and second are elements (not attributes). The | xpath operator it's like a union of nodes.

<xs:element name="exampleElement" type="exampleType">
    <xs:unique name="firstAndSecondDifferent">
        <xs:selector xpath="first | second" />
        <xs:field xpath="." />
    </xs:unique>
</xs:element>

<xs:complexType name="exampleType">
    <xs:sequence>
        <xs:element name="first" type="xs:integer" />
        <xs:element name="second" type="xs:integer" minOccurs="0" />
    </xs:sequence>
</xs:complexType>

The following element is valid (first and second have different values):

<exampleElement>
    <first>1</first>
    <second>5</second>
</exampleElement>

The following element is valid (no second element present):

<exampleElement>
    <first>1</first>
</exampleElement>

The following element is not valid (first and second have the same value):

<exampleElement>
    <first>1</first>
    <second>1</second>
</exampleElement>

This can't be done with attributes because selector xpath doesn't allow to use attributes so "@first | @second" it's not a valid value of the xpath attribute of a selector.