CODEWITHSUNDEEP
xsd
Collin Arnold
Collin Arnold

Reputation: 229

How can I represent a sequence of an element with coupled attribute types in XSD?

I have the following requirements and am trying to determine how best to model the XSD to represent these requirements.

I have many instances of an XML element, say <box>. Each <box> has a required attribute t="[box-type]" and each box with a specific type, say t="tall" has another required attribute v="10" which represents the height of the tall box. All <box>es have both t and v attributes, but the restriction on what values are accepted for their v attributes depends on the value of their t attribute.

For example, take the following XML:

<box t="tall" v="10"/>
<box t="named" v="George"/>
<box t="colored" v="green"/>

Now, in my XSD I need to be able represent a sequence of such elements. My thought was to do something like the following which just lists out all of the allowed box types in my sequence (at the end of the following snippet):

<xsd:simpleType name="box_types">
    <xsd:restriction base="xsd:token">
        <xsd:enumeration value="tall" />
        <xsd:enumeration value="named" />
        <xsd:enumeration value="colored" />
    </xsd:restriction>
</xsd:simpleType>

<!--Box base-->
<xsd:complexType name="box_type">
    <xsd:attribute name="t" use="required" type="box_types"/>
    <xsd:attribute name="v" use="required"/>
</xsd:complexType>

<!--Box concrete types-->
<xsd:complexType name="tall_box_type">
    <xsd:complexContent>
        <xsd:extension base="box_type">
            <xsd:attribute name="t" fixed="tall" use="required"/>
            <xsd:attribute name="v" type="xsd:int" use="required"/>
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>

<xsd:complexType name="named_box_type">
    <xsd:complexContent>
        <xsd:extension base="box_type">
            <xsd:attribute name="t" fixed="named" use="required"/>
            <xsd:attribute name="v" type="xsd:string" use="required"/>
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>

<xsd:complexType name="colored_box_type">
    <xsd:complexContent>
        <xsd:extension base="box_type">
            <xsd:attribute name="t" fixed="colored" use="required"/>
            <xsd:attribute name="v" type="xsd:token" use="required"/>
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>

<!--And finally, the place where boxes show up-->
<xsd:complexType name="box_usage">
    <xsd:sequence>
        <xsd:element name="box" type="tall_box_type"/>
        <xsd:element name="box" type="named_box_type"/>
        <xsd:element name="box" type="colored_box_type"/>
    </xsd:sequence>
</xsd:complexType>

Unfortunately, that is not a valid XSD - VS gives me the several errors, the most unfortunate being Elements with the same name and in the same scope must have the same type. Any advice on how I can represent these t/v coupled attribute restrictions in an XSD?

Upvotes: 1

Views: 567

Answers (1)

xan
xan

Reputation: 7731

XML Schema 1.0 can't validate dependencies between values. Your options are:

  1. Change your XML. For instance, use tallBox, colorBox and nameBox as element names.
  2. Validate the general structure with XSD and validate values with program logic (or some other tool like Schematron or an XSLT stylesheet).
  3. Use XML Schema 1.1, which can validate value constraints but is not commonly supported, yet.

Upvotes: 1

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