XSD 1.1 Conditional Type Assignment <alternative test=""> to check if an element hasn't an attribute set?

Question

I would like to ask if someone knows how to make an XSD 1.1 Conditional Type Assignment check if an element hasn't an attribute using the XPath query, e.g.:

<!--inline alternative type definitions --> 
<element name="TimeTravel" type="TravelType"> 
      <alternative test="@direction='Future'"> 
          <complexType> 
              <complexContent> 
              <restriction base="TravelType" 
                         .... 
<!--        some past travel related elements go here --> 
            </complexType> 
       </alternative> 
      <alternative test="@direction='Past'"> 
          <complexType> 
              <complexContent> 
              <restriction base="TravelType" 
                         .... 
   <!--        some future travel related elements go here --> 
            </complexType> 
       </alternative> 
  </element> 
                          OR 
<!--Named alternative type definitions --> 
<element name="TimeTravel" type="TravelType"> 
   <alternative test="@direction='Future' type="FutureTravelType"/> 
   <alternative test="@direction='Past' type="PastTravelType"/> 
</element>

In this example the 'alternative test=""' checks whether the attribute "direction" of the TimeTravel element has a value of "Future" or "Past". How should I write the XPath query to check if e.g. there's no "direction" attribute for the current element?

Pigment

Answer 1

The XPath "@direction" will test for the presence of a direction attribute on the current element:

<alternative test="@direction" type="DirectionType"/>

The XPath "not(@direction)" will test for the absence of a direction attribute on the current element:

<alternative test="not(@direction)" type="NoDirectionType"/>

Note also that the alternative/@test attribute can be omitted altogether to provide a default type.

<alternative type="DefaultType"/>

Update to address CTA subset mode per OP's follow-up question

So this <alternative test="@direction='a_value' and not(@another_attribute)"/> is correct and would make it right?

Yes, but be aware that your XSD processor may use the XPath CTA (Conditional Type Assignment) subset by default. (Xerces, and therefore most Xerces-based tools, do this, for example.) If this is the case, you will get an error that looks something like this:

c-cta-xpath: The XPath expression 'not(@direction)' couldn't compile successfully in 'cta-subset' mode, during CTA evaluation.

c-cta-xpath: The XPath expression '@direction='a_value' and not(@another_attribute)' couldn't compile successfully in 'cta-subset' mode, during CTA evaluation.

To use full XPath 2.0 rather than the CTA subset, configure your tool accordingly. For example, for Xerces, set the following feature to 'true':

http://apache.org/xml/features/validation/cta-full-xpath-checking

In oXygen, there's a checkbox in Options > Preferences > XML > XML Parser > XML Schema that will control the value of the feature for you.

Using full XPath 2.0, yes, you can use and in the manner you suggest in your comment.

Invalidism

Thank you for your explanatory response, just another question, if for example I need to check that the element has an attribute with a particular value and at the same time check if another attribute is absent what can I do? – Pigment

You can use boolean expressions to build up more complicated conditions using and, or, and not. – Invalidism

Thanks for the link! So this <alternative test="@direction='a_value' and not(@another_attribute)"> is correct and would make it right? – Pigment

I am sorry for my ignorance, but what does CTA mean in XPath CTA? Surfed the net but didn't find anything. – Pigment

CTA is Conditional Type Assignment. – Invalidism