Search code examples
xmlxsdxsd-validationxml-validation

XSD to couple values of two XML elements?

My program can return 2 XMLs like:

<RESPONSE>
    <ERROR_ID>1</ERROR_ID>
    <ERROR_MESSAGE>Parse error</ERROR_MESSAGE>
</RESPONSE>

<RESPONSE>
    <ERROR_ID>2</ERROR_ID>
    <ERROR_MESSAGE>Unexpected attribute</ERROR_MESSAGE>
</RESPONSE>

I try write some XSD file to validate if they are ok. Here what I end up with:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="qualified">

    <xsd:element name="RESPONSE" type="Response"/>

    <xsd:complexType name="Response">
        <xsd:all>
            <xsd:element name="ERROR_ID" type="ErrorId"/>
            <xsd:element name="ERROR_MESSAGE" type="ErrorMessage"/>
        </xsd:all>
    </xsd:complexType>

    <xsd:simpleType name="ErrorId">
        <xsd:restriction base="xsd:positiveInteger">
            <xsd:enumeration value="1"/>
            <xsd:enumeration value="2"/>
        </xsd:restriction>
    </xsd:simpleType>

    <xsd:simpleType name="ErrorMessage">
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="Parse error"/>
            <xsd:enumeration value="Unexpected attribute"/>
        </xsd:restriction>
    </xsd:simpleType>

</xsd:schema>

It validates fine but I'm thinking if can I link up error id with error message to not let pass validation file where error id=2 will go with message from error with id=1:

<RESPONSE>
    <ERROR_ID>2</ERROR_ID>
    <ERROR_MESSAGE>Parse error</ERROR_MESSAGE>
</RESPONSE>

There is a good way to do this? My program returns of course a lot more error ids and message.

Maybe a better question is if I should even expect such a validation from XSD?

Solution

  • XSD 1.0 cannot constrain the value of one element based upon the value of another element.

    XSD 1.1 could do so using xsd:assert, however you should reconsider your design...

    Alternative design suggestions:

    1. Don't check the ERROR_ID-ERROR_MESSAGE pairing in XSD.

    2. Concatenate the error id with the error message:

      <Error>1. Parse error</Error>

    3. Used fixed attributes against more specific error element names:

      <ParseError id="1" message="Parse error"/>
<UnexpectedAttributeError id="2" message="Unexpected attribute"/>

    None of these alternative designs require XSD 1.1.