Reciprocality of PartOf relationships

[andyward]

Using the PartOf facet it's possible to state requirements like "All spaces must belong to a zone" using the IfcRelAssignsToGroup relation, and applying the criteria to the IfcSpace.

<specification name="A Space must have a zone" ifcVersion="IFC2X3 IFC4">
  <applicability maxOccurs="unbounded">
    <entity>
      <name>
        <simpleValue>IFCSPACE</simpleValue>
      </name>
    </entity>
  </applicability>
  <requirements>
    <partOf relation="IFCRELASSIGNSTOGROUP">
      <entity>
        <name>
          <simpleValue>IFCZONE</simpleValue>
        </name>
      </entity>
    </partOf>
  </requirements>
</specification>

But is it possible to express the inverse: "All zones must be assigned to at least one IfcSpace"?

<specification name="A Zone must have a space" ifcVersion="IFC2X3 IFC4">
  <applicability maxOccurs="unbounded">
    <entity>
      <name>
        <simpleValue>IFCZONE</simpleValue>
      </name>
    </entity>
  </applicability>
  <requirements>
    <partOf relation="IFCRELASSIGNSTOGROUP">
      <entity>
        <name>
          <simpleValue>IFCSPACE</simpleValue>
        </name>
      </entity>
    </partOf>
  </requirements>
</specification>

i.e. should we be able to test from both the RelatingGroup and RelatedObjects side of the relationship? I haven't seen any documentation or tests that indicate that's possible. Ultimately it's a many-many cardinality so feels like we should be able to test from both sides.