Restriction on values of N elements with XSD

Question

I am looking a way to apply restriction on values of two elements combined with each other. My current schema is:

<xs:simpleType name="CTKOD_EONE">
    <xs:restriction base="xs:string">
        <xs:enumeration value="1" /> 
        <xs:enumeration value="2" /> 
        <xs:enumeration value="3" /> 
        <xs:enumeration value="4" /> 
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="CTKOD_ETWO">
    <xs:restriction base="xs:string">
        <xs:enumeration value="A" /> 
        <xs:enumeration value="B" /> 
        <xs:enumeration value="C" /> 
        <xs:enumeration value="D" /> 
    </xs:restriction>
</xs:simpleType>


<xs:element name="DATA" minOccurs="0" maxOccurs="unbounded">
    <xs:complexType>
        <xs:all>
            <xs:element name="EONE" type="CTKOD_EONE">
            <xs:element name="ETWO" type="CTKOD_ETWO">
        </xs:all>
    </xs:complexType>
</xs:element>

XML example:

<DATA>
    <EONE>1</EONE>
    <ETWO>C</ETWO>
</DATA>
<DATA>
    <EONE>4</EONE>
    <ETWO>D</ETWO>
</DATA>
<DATA>
    <EONE>2</EONE>
    <ETWO>A</ETWO>
</DATA>
<DATA>
    <EONE>3</EONE>
    <ETWO>B</ETWO>
</DATA>

But in my case each DATA must have a restriction on combination of EONE and ETWO. For example:

1 with C  - valid
4 with D  - valid
2 with A  - valid
3 with B  - INVALID!!

Is that possible to have some complex restriction on values of N child elements? Or other way to solve this issue with XSD? Help me please to figure out the possible solution.

Answer 1

It's easy in XSD 1.1 with xs:assert.

It's impossible in XSD 1.0.