What does AverageOfChildren aggregate function in SSAS 2005 actually do?

Question

Folks,
Have any of you been playing around with SSAS 2005 to have worked out
what the AverageOfChildren aggregate function actually does?
I was expecting it to do the equivalent of a simple AVG() with a GROUP
BY in SQL, but it seems to be doing something additional to that.
No-one in the team I work in has been able to work out what exactly it
is doing.
Any info would be appreciated!
Cheers,
Kenneth

Answer 1

This very question was recently discussed in the public SQL Server OLAP newsgroup:
http://groups.google.com/group/microsoft.public.sqlserver.olap/msg/c662e201b99678bc
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 Aggregate Function Average of Children does not work
This behavior could occur because
AverageOfChildren,FirstChild,LastChild,FirstNonEmpty and LastNonEmpty are
semi-additive and treats the Time dimension different from the other
dimensions. Please refer to the following link for details:
http://msdn2.microsoft.com/en-us/library/ms175356.aspx
The description in above link (BOL) is not very clear about
AverageOfChildren, and I have forward this feedback to the proper channel.
The AverageOfChildren only applys when aggregating via Time dimension.  
Actually, when you try to create a new measure in cube, when you select
usage, you could see "average over time" which is for AverageOfChildren.
To get the result of average behavior you want, you may want define a Sum
and a Count measure, then create a calculated measure (in the cube script)
which divides the two base measures.
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