I have an SSAS Tabular model composed of a fact table and 3 dimensions.
I want to understand what is the difference between creating the relationships in the tabular model in advance comparing to import the tables or using a direct query and then create the relationships in Power BI ?

>Solution :

If you DirectQuery to SSAS Tabular, then the measures and relationships should already be included.

Power BI essentially is SSAS Tabular under the hood, so the calculations should be the same whether you build your model in Power BI Desktop or SSAS Tabular. The difference is where you’re running it. If you have SSAS Tabular on a strong server, DirectQuery might be faster than running the computations locally in Power BI Desktop.