Error on snowflake, no workaround

Question

Hello all,
I have a part of my BM which is in snowflake :
MEC date -> vehicle -> invoice
both dimensions tables MEC date and vehicle have their own LTS and their own dimension (hierarchy).
Each dimension table LTS is set to be the lowest level in the dimension
My fact table LTS is set to the lowest level of vehicle, nothing about the date.
I cannot put the date directly in the invoice fact table to turn my snowflake into a star
I have a consistency warning saying that my date dimension table isn't linked to any fact table.(A)
If I add in the fact LTS the lowest level for that date (B), i get an additional error saying my fact table is given an aggregation level to a dimension it is not linked to.
if I don't add the date information in the fact table (B), and I ignore the warning about the dimension (A), I can't run a report using both the date and invoice informations.
Can anybody please tell me what is the proper way to build this snowflake model?
Thanks
Ced

Answer 1

Hi Matt!
Glad to read you again!
I agree with you that in this simple example, I should be able to make this a star schema.
but :
- on a functional point of view, this date is an attribute of a vehicle, not of an invoice. But let's ignore this.
- this problem is the same as one we have in another part of the BM, which is much more complex. In this complex BM, I can't use star schemas because it removes some joins we need in order to perform some reports.
This is why I'm looking for another way to proceed.
If you have time to spend on the complex BM, here is a simplified description :
* in the physical layer, I have:
- a calendar table with multiple aliases to be used with each dates in the following,
- an invoice header table
- an invoice detail table
with
some header date -> header table -> detail table
some detail table -> detail table
* in the logical layer (stars), i have:
- my calendar dates with their dimensions
- an invoice dimension table with the two sources (header + detail) + its dimension
- an invoice header fact table
- an invoice detail fact table
header date -> header fact
invoice dim -> header facts
invoice dim -> detail facts
detail date -> detail facts
I mus be able to query details facts while showing or filtering the header date. In such a configuration, you'll understand it isn't possible as there isn't any relationship between the detail facts and the header date. This is why the header date should be kept as a dimension of the invoice dimension, which is similar to my basic example.
Unless I went wrong somewhere?
Thanks!
Ced.
Message was edited by:
ced