Question

Is there a way in an xsd schema to require that an element have another element somewhere as a descendant?

For example, element parent requires a descendant desc. This is valid:

<parent>
  <a>
   <b>
     <desc></desc>
   </b>
  </a>
</parent>

As is this:

<parent>
  <c>
    <desc></desc>
  </c>
</parent>

but this isn’t:

<a>
  <parent>
    <b/>
  </parent>
</a>

The potential child elements for parent are many and complicates, so it would be difficult to enumerate every possible valid configuration.

Something like the key/selector schema elements seems like it would work, where I could provide an xpath expression defining the valid locations for desc element, but all of the examples I’ve found are aimed at matching up the value of attributes.

Answer 1

No, (almost) all XML Schema validation is shallow, called “local” in the spec. Here’s one excerpt that emphasizes type validation as “local” validation.

Element Validated by Type If an
element information item is ·valid·
with respect to a ·type definition· as
per Element Locally Valid (Type)
(§3.3.4), [it is marked as] ·validated·.

The only exception is for the identity constraints like uniqueness and key-references which have a broad scope in an XML document but narrow uses.