When you create a user-defined property type there are two things to keep in mind.

1. The user-defined property should be transient.
2. The user-defined property must have a data-type defined or the item that contains this property will not be displayable in the ACC.

Here is an example of a user-defined property type.

<item-descriptor name="foo" display-property="name" display-name="Foo">
  
 <property name="bar" property-type="com.betweengo.Bar" data-type="string"/>
 
 <table name="foo" type="primary" id-column-names="id">
  <property name="id" data-type="string"/>
  <property name="name" column-names="name" data-type="string"/>
 </table>
 
</item-descriptor>

To learn more, User-Defined Property Types. Note that in the ATG documentation the example for the user-defined property does not define a data-type. This is probably a documentation bug.