Question

Consider the following (poorly designed?) XML document:

<?xml version="1.0" ?>
<command_result>
<param name="protocol_version" value="3"/>
<param name="player_state" value="navigator"/>
</command_result>

What I want to do is create an XML schema (XSD format) that specifies the datatype of the value attribute based on the actual value of the name attribute.

Example (pseudocode):

if (param name = "protocol_version") then (param value type="xs:integer")
if (param name = "player_state") then (param value type="xs:string")

Is there a way, without modifying the source XML, to introduce such a conditional statement in the schema file? I’ve looked at various solutions, but all of them required changes to the source somehow (e.g. setting xsi:type).

EDIT

My current schema:

<?xml version="1.0" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="command_result">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="param" minOccurs="2" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:attribute name="name" type="xs:string" use="required"/>
                        <!-- the following line needs to be modified somehow -->
                        <xs:attribute name="value" type="xs:string" use="optional"/>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

Answer 1

I don’t think this is possible. The only way I can think of is something like this:

<schema xmlns="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.example.org/schema"
    xmlns:tns="http://www.example.org/schema" elementFormDefault="qualified">

    <element name="command_result">
        <complexType>
            <sequence>
                <choice>
                    <element name="param" type="tns:protocol_version_type" />
                    <element name="param" type="tns:player_state_type" />
                </choice>
            </sequence>
        </complexType>
    </element>

    <complexType name="protocol_version_type">
        <attribute name="name" type="string" fixed="protocol_version" />
        <attribute name="value" type="integer" />
    </complexType>

    <complexType name="player_state_type">
        <attribute name="name" type="string" fixed="player_state" />
        <attribute name="value" type="string" />
    </complexType>
</schema>

But apparently this is not allowed. When I validate this schema in Eclipse, it gives me the following errors:

• cos-nonambig: “http://www.example.org/schema”:param and “http://www.example.org/schema”:param (or elements from their substitution group) violate “Unique Particle Attribution”. During validation against this schema, ambiguity would be created for those two particles.
• cos-element-consistent: Error for type ‘#AnonType_command_result’. Multiple elements with name ‘param’, with different types, appear in the model group.

As you can see, you can’t have two elements with the same name but with a different type. But this is what your XML requires.

Edit: You can’t even define a simpler schema like this:

<element name="command_result">
    <complexType>
        <sequence>
            <element name="param" type="tns:proptocol_version_type" />
            <element name="param" type="tns:type2" />
        </sequence>
    </complexType>
</element>

In this version, no <choice> is given, meaning your parameters would have to appear in the given order. But while this removes the nonambig error, the element-consistenterror remains.