Question

I’m trying to define an element type in XSD, for which i want an optional attribute, which if present can either contain a float, or be empty (but still present).

i.e:

<xs:element name="MyElement">
    <xs:complexType>
        <xs:attribute name="optionalFloatAttribute" type="xs:float" use="optional"/>
    </xs:complexType>
</xs:element>

Needs “fixing” to allow all of the following xml:-

<MyElement/>
 or
 <MyElement optionalFloatAttribute=""/>
 or
 <MyElement optionalFloatAttribute="3.14159"/>

The only way I can see of doing this is to change type to xs:string, and use xs:restriction with a regular expression. But this doesn’t seem very ideal to me. Is there a better way?

And I have to be able to support these variations of the xml – the program and existing xml is legacy, and I am trying to back-create a schema to match the myriad variations I see in what we have to regard as valid xml.

Answer 1

I don’t think there’s a way to handle this and use xs:float. Fundamentally it comes down to the fact that empty string isn’t a valid number. You’d either normally expect a value of 0, or for the element to be missing altogether. There’s a good explanation as the answer to the following question:

Empty elements for primitve datatypes forbidden in XSD

It seems that the option of using xs:string and a regexp might be your best plan.