[Mondrian] Date dimensions and attribute-hierarchies in mondrian 4

[Julian Hyde]

On Apr 10, 2012, at 7:47 AM, James Dixon wrote:

On the call yesterday you mentioned that you would do ‘day of week’ as part of a date dimension instead of a separate attribute. My problem with date dimensions is that I often want to put year on a different axis from month, week, or day of week. I have not been able to do this with Analyzer using a date dimension. I thought this was an MDX limitation. Is there something in the new Mondrian version that lets me put different levels of a date dimension on different axes?

James,

In old versions of mondrian (consistent with SSAS 2000), you weren't allowed to have the same dimension on more than one axis. (E.g. you couldn't have Time.Weekly on columns and Time.Yearly on rows.)

A couple of years ago I changed it (consistent with SSAS 2005 and later). Now you can have the same dimension on different axes, but you can't have the same hierarchy on different axes. So,

select [Time.Weekly].[Year] on 0
 [Time].[Year] on 1
from [Sales]

is valid.

In Mondrian 4, the attributes in the date dimension would all have their own hierarchy. You don't reference attributes directly from MDX, but you reference the hierarchies and levels. For example, [Time].[Year] is the hierarchy for the "Year" attribute, and [Time].[Year].[Year] is its level. You can put these hierarchies wherever you want. E.g.

select [Time].[Year].[Year.Members * [Time].[Quarter].[Quarter].Members on 0,
 [Time].[Day of Week].Members on 1
from [Sales]

You can also use Year and Quarter to build levels in the [Time].[Monthly] hierarchy, but then you can't use them on on separate axes:

select [Time].[Monthly].[Year].Members on 0,
 [Time].[Monthly].[Quarter].Members on 1
from [Sales]

is illegal.

Benny,

I think that analyzer should help if someone wants to "break" a hierarchy. If they try to build a query like that, analyzer should ask them whether they want to use attribute hierarchies instead. It would rewrite to

select [Time].[Year].[Year].Members on 0,
 [Time][Quarter].[Quarter].Members on 1
from [Sales]

Do you agree?

I've logged http://jira.pentaho.com/browse/ANALYZER-1184 for this.

Julian
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