Transformation of Relationships across component borders
Transformation of Relationships across component borders were not implemented because of time reasons. Additionally, Relationships that extend across component borders are of limited use for a model used at design-time. The reasoning is that for performance prediction the callstack model builds all possible call paths incrementally starting from a user call to resolve parameter dependencies. It resolves dependencies for ModelVariables as they appear in a called service. First Relationships are tried to be solved and failing that setting the ModelVariable to the fallback value for InfluencedVariables or null for InfluencingVariables. In the different paths a ModelVariables can have different values, depending on the values on the call paths that have already been resolved. However, a ModelVariable is allowed to be the dependent in a Relationship at most once. That means that the ModelVariable has the fallback value for all callpaths in which the path does not lead through the component where the InfluencingParameter of the Relationship resides. As only one explicit Relationship is allowed, the influenced ModelVariable can depend only on the variables specified in the Relationship. If the variable is outside of the component the Relationship makes the connection static and the variable can not be influenced by any other variable. This may be the intention in some cases, however we consider it rare.
Note: Taken from thesis Adrian Hildebrandt