Question

In using XML Schema 1.1, I’d like to define an attribute group that occurs entirely together, i.e. all the attributes in the attributeGroup are either present or not-present. In the following example, I’d like <anelement> to have both attributes (attr_one and attr_two) present or neither attribute present, never only a single attribute present.

<attributeGroup name="attrgroup">
  <attribute name="attr_one" />
  <attribute name="attr_one" />
</attributeGroup>

<element name="anelement">
  <complexType>
    <attributeGroup ref="attrgroup" />
  </complexType>
</element>

As I understand it, XML Schema 1.0 cannot specify these attribute relationships (correct?). What is the best way to specify them in XSD 1.1? I figure that I can use assert to specify the relationship, something like the following:

<element name="anelement">
  <complexType>
    <attributeGroup ref="attrgroup" />
    <assert test="(@attr_one and @attr_two) or not(@attr_one or @attr_two)" />
  </complexType>
</element>

But I was hoping there was something added to 1.1 that would allow me to specify the relationship using the existing language, e.g. a use attribute on attributeGroups. What is the best way to specify this relationship in XML Schema 1.1?

Answer 1

Assertions are the way to do this. A simpler formulation is

test="exists(@attr_one) = exists(@attr_two)"

or you could do

test="count(@attr_one|@attr_two) != 1"