xml mapping

Hi,

I have a question about Castor mapping files:
I have an XML file of the following form:

<a>
  <b> </b>
</a>
<a>
  <c> </c>
</a>
<a>
  <d> </d>
</a>
So actually, the element in <a> is a choice between b, c and d

I have a java class structure like

class Ja {
  Jx x;
}

abstract class Jx{}

class Jb extends Jx{}
class Jc extends Jx{}
class Jd extends Jx{}

I'm trying to map the xml file above to the java structure with one mapping file.
Is this possible, and if yes, how?

Could you help me with this problem?

Regards,

Abed