property restriction

Hello,

I'd like to restrict a property on a class so that,

this should be legal:

[
       a ex:Participation;
       ex:inGroup _:org1;
       foaf:mbox <mailto:bill@example.com>
       ex:role [
          a ex:Role;
          foaf:mbox <ceo@example.com>;
          ex:offGroup _:org1;
       ]
]
 
while this should not be legal:

[
       a ex:Participation;
       ex:inGroup _:org1;
       foaf:mbox <mailto:bill@example.com>
       ex:role [
          a ex:Role;
          foaf:mbox <ceo@example2.com>;
          ex:offGroup _:org2;   <----- Should be a contradiction
       ]
]


Both the ex:inGroup and the ex:offGroup property have a cardinality 
restriction of 1 on their respective domain, but furthermore the range 
of ex:role should be restricted to ex:Roles with an ex:offGroup property 
with the same value as the ex:inGroup property of the ex:Participation, 
or respectively the ex:inGroup property should be interferable from 
ex:offGroup property of the property-value of any ex:role property.

any help is appreciated...

reto