PRR — Change model to use Expression in lieu of OpaqueExpression (nherited from UML2)

Change model to use Expression in lieu of OpaqueExpression (nherited from UML2) - following FTF face2face discussions on relevance of Expression vs OpaqueExpression. Affects: pg 9 Fig 7.1 PRR metamodel pg 11 Fig 7.3 PRR ProductionRule Classes pg 11 Fig 7.4 PRR RuleVariable Classes pg 12-13 7.4.6 Computer Executable Rule pg 13 7.4.8 Variable pg 14 7.4.9 ProductionRuleset pg 15 7.4.11 RuleCondition pg 16 7.4.12 RuleAction pg 16 7.4.15 RuleVariable pg 18 Fig 7.6 Metamodel for PRR OCL pg 43-44 Annex A Complete Metamodel In all the above, the OpaqueEpression is directly replaced by Expression with no other changes.

Change model to use Expression in lieu of OpaqueExpression (inherited from UML2) -
following FTF face2face discussions on relevance of Expression vs OpaqueExpression