Working with relationships in PowerPivot and SSAS BISM Tabular

Relationships in PowerPivot and SQL Server Analysis Services BISM Tabular can be a bit tricky. It is easy to start with a few simple ones only to end up stuck at some point trying to figure out why table values are not rolling up across relationships as you would expect.

Particularly with PowerPivot, it is easy to get the feeling you can just throw some tables are it, connect them and you should be ready to go.