Two time dimensions in one cube

Question

Hi all,
I have the requirement to create a cube for customer mgmt reports. People want to report on registrations and terminations of customers.
So in my cube I need two references to my time dimension (called dim_time). I tried it out and owb accepts the two references to dim_time, automatically renaming the second dimension to dim_time_1. Deployment and loading is also fine.
So from a testing perspective this seems to be the right way of doing it. Has anyone else done something like this and did you see any problems later on?
I want to be save before I go to production.
Another question is about outer join of the second dim_time reference for termination date. All people have a registration date, but most (hopefully) don’t have a termination date. But all of them shall be loaded to the cube. I have not seen a possibility to influence the joins at the cube operator. What’s possible there ?
Regards,
Knut

Answer 1

In order to do two references to the same dimension, you could create two roles in the time dimension. Then, in the cube you can refer to each role. Actually, it's the same you have done, the only difference is using roles make the model easier to understand, because you can give a friendly name to each role.
The second point is about referencing a null date. I think there is no way to do that using the cube object. In these cases, I use to create a date like '31/12/9999' and doing a reference to that. Inside the map you can use an expression with something like that: to_date(NVL(your_date, '31129999'), 'ddmmyyyy'). And, of course, do not forget to insert this date in the dimension.
It's not common to have null data in DW. Any exception should be identified and documented, for example, "Not Available", "Unknown", etc.