Defining recursive elements?

I'm not sure if the subject is accurate, but I'm trying to author an
XSD that allows a certain complex type to be nested within itself to
an arbitrary depth.

A simple example would look like this:

<?xml version="1.0" encoding="utf-8" ?>
<part serial="00000001234">
  <part serial="00000001234">
    <part serial="00000001234">
    </part>
    <part serial="00000001234">
    </part>
    <part serial="00000001234">
      <part serial="00000001234">
      </part>
      <part serial="00000001234">
        <part serial="00000001234">
        </part>
      </part>
    </part>
  </part>
  <part serial="00000001234">
  </part>
</part>

Any "part" can contain any number of other parts.

Is it possible to validate this structure without putting an arbitrary
limit on the maximum depth?