Dynamic attribute in element XSD Schema

Question

It is possible to add dynamic attribute in <element> for example I have a <A> element it have a fixed attribute name mode

<A mode="ENABLE"> <!-- ENABLE or DISABLE-->

if mode is enable then it will add some more dynamic attribute in element `<A>`

like

<A mode="ENABLE" attr1="abc" attr2="xyz">

if mode is disable then it will like this .

<A mode="DISABLE" attr3="abc" attr4="xyz">

That means attribute mode is fixed and attr1,attr2,attr3 and attr4 depend on values of mode attribute

mode - Fixed attribute.

attr1,attr2,attr3 and attr4 - Dynamic attribute depend on value of mode

Please give me suitable example.

Answer 1

To allow attributes depending on the contents of other attributes you need XSD 1.1 (or some XSD 1.0 extension such as Schematron). In XSD 1.1 you can use an assertion xs:assert where you declare the rules for the complex type using XPath.

To validate this instance:

<modes>
    <A mode="ENABLE"  attr1="abc" attr2="xyz" />
    <A mode="DISABLE" attr3="abc" attr4="xyz" />
</modes>

You can use a XSD like the one below:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"
    xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning" vc:minVersion="1.1"> 

    <xs:element name="modes">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="A" minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <xs:attributeGroup name="enabled-attributes">
        <xs:attribute name="attr1" type="xs:string" use="optional"/>
        <xs:attribute name="attr2" type="xs:string" use="optional"/>
    </xs:attributeGroup>

    <xs:attributeGroup name="disabled-attributes">
        <xs:attribute name="attr3" type="xs:string" use="optional"/>
        <xs:attribute name="attr4" type="xs:string" use="optional"/>
    </xs:attributeGroup>

    <xs:element name="A">
        <xs:complexType>
            <xs:attributeGroup ref="disabled-attributes"/>
            <xs:attributeGroup ref="enabled-attributes"/>
            <xs:attribute name="mode" use="required">
                <xs:simpleType>
                    <xs:restriction base="xs:NMTOKEN">
                        <xs:enumeration value="ENABLE" />
                        <xs:enumeration value="DISABLE" />
                    </xs:restriction>
                </xs:simpleType>
            </xs:attribute>
            <xs:assert test="(@mode='ENABLE'  and @attr1 and @attr2 and not(@attr3) and not(@attr4)) 
                          or (@mode='DISABLE' and @attr3 and @attr4 and not(@attr1) and not(@attr2))"/>
        </xs:complexType>
    </xs:element>
</xs:schema>

I placed the attributes for each mode in a separate attribute group. Your mode attribute is not actually fixed but can have two values, so I used an enumeration to restrict it to those two values.

The line that requires XSD 1.1 is the xs:assert line. The XPath expression is evaluated relative to the elements in the complex type. If the expression is true, it will validate.

Validation will fail otherwise. These A nodes will both fail validation:

<modes>
    <A mode="DISABLE" attr1="fgs" attr4="hjs" />
    <A mode="ENABLE"  attr3="fgs" attr4="hjs" /> 
</modes>

Update: I added the not() clauses above, since the assertion was incomplete as you noted. Now this validates to false:

<A mode="DISABLE" attr1="fgs" attr2="hjs" attr3="fgs" attr4="fgs"/>

You can also use other criteria (it's a XPath subset), such as the number of attributes, for example if you have a lot of attributes and want to avoid a lot of not() clauses you can use:

@mode='ENABLE' and @attr1 and @attr2 and count(@*) = 3

that will restrict the total number of attributes to 3.