Populating Attributes based on two other pm Attributes

PointsWell

I am having a logic problem and it is my misunderstanding that would appear to be causing it.

I have a BO (Contract) with 3 PM attributes:

1 - Territory - which is a pm relationship to a Table Territories. An attribute of Territories is another pm relationship Countries.
2 - Excluded - is a pm relationship also to Countries
3 - Countries - which is a pm relationship to, you. guessed Countries.

What I am trying to achieve is a population of the Countries attribute based on all the Countries in Territory.pm_Countries that are not contained within Excluded and for this to refresh each time either Territories is updated or Excluded is updated.

The Business Rule that I had built is:
If Contract.pm_Territories WAS CHANGED OR Contract.pm_Except WAS CHANGED Then
Contract.pm_Countries=(Contract.pm_Territories.pm_Country WHERE ( NOT(Contract.pm_Territories IN Contract.pm_Except)))

But I am getting an error:
Syntax error at token "." (column 10).

Column 10 is the period between Contract.pm_Countries on the second line, my experience to date has been that when I get these sorts of errors I have approached the problem from the wrong direction and should be using a different approach. Could someone point me in the correct direction please.

Thanks in advance

tford

Not your exact scenario, but perhaps concepts here will be useful to you:

https://forum.awareim.com/d/5274

PointsWell

Thanks. As I said coming at it from the wrong direction.

But now I have another question...

Now that I have realised I need to first find the Territories referred to in the field then find the Countries that are contained within that Territory's list of Countries. But I am getting an error Value for path LuTerritories.pm_Countries could not be resolved. So I am thinking I have misunderstood the structure here

If LuTerritories.pm_Countries is a multi value peer does this resolve itself as a list?

My logic was
FIND Territories
FIND Countries where they are IN Territories.pm_Countries

but this is obviously flawed.

If Contract.pm_TerritoriesExclusive WAS CHANGED OR Contract.pm_Except WAS CHANGED Then 
FIND LuTerritories WHERE (LuTerritories IN Contract.pm_TerritoriesExclusive)
 FIND LuContCtry WHERE (LuContCtry IN LuTerritories.pm_Countries) AND NOT(LuContCtry IN Contract.pm_Except) 
Contract.pm_CountriesExclusive=LuContCtry