Robert Angel wrote:Dimension X - a normal dimension that joins to the detail level of the combined factDimension Y (based on fact details, with 3 tiers in hierarchy, Total, Header and Detail from top to bottom)Fact (based on Fact detail and fact header in LTS)

Not sure about that model unless there's something I'm not grasping here. Why the two dimensions? This over-complicates things. If you really want to have two separate logical dimensions for header and detail then they should be header and detail full stop - so additional hierarchy levels. OR you go the way of your Dimension Y with the levels and basically each level representing one of the two fact attribute aliases for use as dimension LTSs. Header alias for the attributes at header level and ditto for the detail.

I'm searching my RPDs for a sample model of this.