What's the "Parent Child" property of a regular dimension used for?

[sokhaty]

Hi,
I'm trying to locate any information on the "Parent Child" property of a regular dimension.
We are planning to upgrade to 8.4 from 1.1 and start using its DMR features.

I tried searching Cognos support site and asked the trainer in my FM class, but wasn't able to find any useful information so far.

It would be nice to have a sample of when and how this property should be used.

Thanks in advance,
Seva.

[goose]

I dont have access to FM but if my memory serves me correctly this will tell Cognos that the dimension models a parent-child hierarchy i.e. parent and child members are in the same table, like modeling a tree structure in one table.

http://dev.mysql.com/tech-resources/articles/hierarchical-data.html

[sokhaty]

Well, that's not too helpful. After spending last 10 years working with hierarchical data, I generally understand what parent-child relations are and how to flatten and balance hierarchies for reporting.
Unfortunately, in a DMR environment flattening/balancing isn't all too performing (and the current requirement is to report off of live data).

Question is what effect, if any, "Parent Child" property has on query generation in FM (what the heck it's there for). The hope being that FM 8 is smart enough to generate minimal required amount of those "flattening/balancing" joins.

So far, setting or clearing this property doesn't seem to affect anything in FM - no changes is the column roles, no changes in the resulting query.

If it's a undocumented and unsupported property, what's the point in exposing it in the FM UI.

Thanks,
Seva.

[JGirl]

I could be wrong but I'd always assumed is was a property that was only relevant when using a SAP BW in FM...

I've never used it though.

J

[sokhaty]

I had a chance to speak with one of the Cognos developers. This turned out to be one of those cases, when feature was supposed to be implemented, but didn't make it into release, yet some artifacts of it still leaked out into the world.

As of now the attribute does not affect anything at all.

[blom0344]

Well, that's not too helpful. After spending last 10 years working with hierarchical data, I generally understand what parent-child relations are and how to flatten and balance hierarchies for reporting.
Unfortunately, in a DMR environment flattening/balancing isn't all too performing (and the current requirement is to report off of live data).

Question is what effect, if any, "Parent Child" property has on query generation in FM (what the heck it's there for). The hope being that FM 8 is smart enough to generate minimal required amount of those "flattening/balancing" joins.

So far, setting or clearing this property doesn't seem to affect anything in FM - no changes is the column roles, no changes in the resulting query.

If it's a undocumented and unsupported property, what's the point in exposing it in the FM UI.

Thanks,
Seva.

I can imagine that fully supporting hierarchical structures is one hell of a feature, but I think BI vendors ran into a wall pretty fast when thinking this through. I can imagine a solution for say 1-3 levels deep and generating the SQL in those cases, but what with unknown number of levels. The major RDBMS vendors have all implemented their own code to this type of recursion-solution (no ANSI standards AFAIK), which must have been too much to solve from the Cognos point of view. And if they had solved this, you would still have to cope with low to abysmal performance (especially in your case with live data)

By the way, the link by Angus is a very nice article!!