I'm now working on a data warehouse project with SSAS 2008 R2 (Sql Server Analysis Services). It is very refreshing to do something different after doing MS-Access for so long.
While designing the dimensions in Analysis Services I had the following problem: working in a Financial Company, every client has a client group. Sometimes it is the same client group as the client, and sometimes it isn't. Pretty classic material:
John & Jane Smith (account id: 1) and John Smith (account id 2) both belong to the same "client group" of John & Jane Smith. So far nothing special: the dimClient table has a self referencing attribute to dimClient with the id of dimClientGroupId. The problem arises when I need to group by properties of the client group, and not by the client itself. Sometimes the adviser for "dimClient" is different then the adviser of "dimClientGroup", and the business needs to view the data by the Client Group, and not by the Client.
So I have quariable attributes that are different in different parent-child levels and I need to present the data properly. I tried using the "client group adviser" as an attribute to the client but it didn't work. It also didn't group the data correctly.
So, how do I use the attributes of the parent dimension in a self-referencing dimension?(Please note: using "self referencing" is better than "parent-child", because then you get to all sort of parenting material; useful, but not what I'm looking for right now!)
Generally, it is advised against using too many parent-child hierarchies in Analysis Services, unless "there's a genuine business requirement" (which happens to be the case).
So, after designing all the dimensions I had to link the "adviser" dimension to the "client" dimension. That was easy (and maybe even done automatically) as every client has an adviser. Now I had to link the "adviser" dimension to the "client group" dimension and this is where I got stuck (after all, "client group" is a self-referencing dimension and is treated by SSAS differently!).
My solution has two levels. I might change between them in the future, as there are no guarantees that my first level will continue to work.
Using "referenced dimensions" I linked the "adviser" dimension to "client".
Now, I've linked the "client" dimension to "client" again and - voila! - I have the "client group" dimension and I can view in the cube the "client group.adviser" dimension and filter by it. A warning: trying to deploy the cube generates an error: "Errors in the metadata manager. The 'Dim Client Group Id' intermediate granularity attribute of the 'Dim Client' measure group dimension does not have an attribute hierarchy enabled.". Nevertheless the cube can still be processed and view from the SSMS - Analysis services, and the numbers are correct.
There is a different solutions to the same problem that is suggested in here (under the "parent-child Hierarchies" short section):
As the numbers of Hierarchies in this business model is fixed (every client has one and only one client group), Creating a bridge table of "portfolio client" which includes only the client and the client group (both are foreign keys to the "dim client" table) and again, using it as a reference dimension as follwos:
[fact]portfoio -> [dim]portfolio client ->[dim] Client Group ->[dim]Adviser sorts this problem in an even clearer manner and without ugly error messages. A good explanation about bridge table could be found in here (they bought me with the term "Graph Theory").