Often time you will come across scenario where in presentation catalog you have 2 or more fact tables and couple of dimensions. And not all the fact tables are joined with all the dimensions.
And when you just query the data out of dimension which is not joined to a fact table. It will give you an error like ..Can not navigate to the fact table.
Matter of fact is : Whenever you query the data just from the dimension it does not just read the data from dimension but it join that dimension with the fact and then get the data from dimension. Pretty weird huh…
So to resolve this what you will need an implicit column in presentation catalog so whenever you query data from dimension it goes through the table where you have defined an implicit column.