Ragged Hierarchies, HideMemberIf and MDX Compatibility

Here’s something that I suspect a few people out there will be surprised I didn’t know – but as far as I’m concerned, if I didn’t know it then it’s worth blogging about.

Anyway, it regards ragged hierarchies, the HideMemberIf property and the MDX Compatibility connection string property. Now you probably know that if you want to turn a user hierarchy into a ragged hierarchy (perhaps to avoid using a parent child hierarchy) you need to use the HideMemberIf property on the user hierarchy. For example, imagine you were using the following SQL query as the basis of your customer dimension:

SELECT        ‘UK’ AS Country, ‘Bucks’ AS State, ‘Amersham’ AS City, ‘Chris Webb’ AS Customer
UNION ALL
SELECT        ‘Italy’ AS Country, ‘BI’ AS State, ‘Biella’ AS City, ‘Alberto Ferrari’ AS customer
UNION ALL
SELECT        ‘Vatican’ AS Country, ‘Vatican’ AS State, ‘Vatican’ AS City, ‘The Pope’ AS customer

We could build a dimension off this with attributes for Country, State, City and Customer, and for two out of our three customers that would be fine. However the Pope lives in the Vatican, which is (at least for the purposes of this exercise) a Country with no concept of City or State; and in the case of customers who live in the Vatican, we just want to be able to drill down on the Country ‘Vatican’ and see all of the Customers who live there without drilling down through a meaningless State and a City.

So what we can do is build a user hierarchy on our dimension with levels Country, State, City and Customer, and on the lower three levels set the HideMemberIf property to OnlyChildWithParentName:

Then, with any sensible client tool, we can connect to the cube and browse the dimension as we want:

I saw ‘sensible’ client tool, because of course this only works if you set:
MDX Compatibility=2
…in the connection string. And of course Excel 2007 hard-codes MDX Compatibility=1 in the connection string and doesn’t allow you to change it, so you can’t use ragged hierarchies properly.

This much I knew.

However, what I didn’t realise until last week when I was moaning about this to TK Anand from the SSAS dev team at PASS, is that for some ragged hierarchies you don’t need to set the MDX Compatibility connection string property at all.

For example, if in our case we duplicate the Customer upwards rather than the Country downwards, like so:

SELECT        ‘UK’ AS Country, ‘Bucks’ AS State, ‘Amersham’ AS City, ‘Chris Webb’ AS Customer
UNION ALL
SELECT        ‘Italy’ AS Country, ‘BI’ AS State, ‘Biella’ AS City, ‘Alberto Ferrari’ AS customer
UNION ALL
SELECT        ‘Vatican’ AS Country, ‘The Pope’ AS State, ‘The Pope’ AS City, ‘The Pope’ AS customer

…and then build the dimension, setting HideMemberIf on our user hierarchy to OnlyChildWithParentName, we can get the result we want without setting the MDX Compatibility property. Here’s a screenshot of this new dimension in Excel just to prove it:

The difference here is that we’re hiding all members below the State level right down to the bottom of the hierarchy, rather than hiding members somewhere in the middle of the hierarchy. Truly, this is one of those “Doh, if only I’d known!” moments… this at least means that in some of the scenarios where you’d use ragged hierarchies you can get them to work with Excel, even if it means that we have to hack the data (‘The Pope’ is a Customer, not a State or a City). On the other hand there are plenty of scenarios where you do need to hide members in the middle of a hierarchy, and frankly I don’t see why Excel 2007 can’t set MDX Compatibility=2 in its connection string so they work properly.