MAJOR FLAW IN COGNOS 8 - Framework Manager joins 1

[andygeorge]

Hi,

I have discovered a major flaw in Cognos 8.

In the modelling tool - Framework Manager - Cognos have created 2 new types of objects
- Regular Dimensions (Query Subjects with Dimension Hierarchy functionality)
- Measure Dimensions (Facts essentially whereby scope can be set at different different dimension levels).

The flaw is as follows:

RELATIONSHIPS INSERTED BETWEEN MEASURE DIMENSIONS AND REGULAR DIMENSIONS DO NOT WORK!!!!

In fact they work for single level hierarchies - but as soon as you create a proper multi-level regular dimension and try to drill down in query studio/report studio, the server attempts a cross-product join i.e. the join is not used.
Joins performed at underlying query subject levels will work, as shown in the sample (simple) Cognos models - but you cannot create your relationships in this way if you have an Enterprise solution whereby FM models are split into different business areas and these 'database views' are linked together via linked segments into each 'datamart' model - with this approach you need to be able to join the dimension objects directly (regular and measure dimensions) at Data-Mart level.

Has anyone else encountered this ridiculous flaw? Can anyone else confirm my findings ?? I've reported it to Cognos, but they are keeping suspiciously quiet on this matter at the moment......

I'm sure Business Objects would love to hear about this one......

Regards,
Andy George
BI Consultant

 

[JGirl]

I wouldnt consider this a 'ridiculous flaw' as much as a 'design feature'.

The relationships between the dimensional query subjects should be handled by the underlying query subjects in the layer that precedes the dimensional layer (as these have determinants etc). The dimensional query subjects in the model then have 'scope relationships' created between them which depend on the underlying relationships already being created in the previous layer.

The best practice approach is to include relationships in the datasource layer, build the dimensions / facts from the data source layer, and then edit/build the 'Scope relationships' in the dimensional layer of the project (as per the cognos examples). To implement this at your site, you might need to add another layer of query subjects between the data source layer and the dimensional layer to handle these relationships.

Additionally, you could use a relational model instead of a dimensional model.

J

 

[andygeorge]

JGirl - thanks for the response, however if this is not a flaw then please can you explain the following:

1) Framework Manager provides the user with the option of creating relationships between the objects (measure/regular dimensions). In addition performing a verification on the model does not pick up any errors once the relationship is in place.

2) The joins are actually picked up with one level hierarchy dimensions. But fail only when a drill-through on a multi- level hierarchy is performed.

3) As for the 'best practise' approach given in the sample models - I'm afraid that Cognos seem to have forgotten about their concept of 'linked-segments'. Our implementation is fairly large and hence we utlized the linked-segment functionality provided in ReportNet ie. we have multiple RN models which hold various sets of conforming query subjects. This allows different developers to work on different models at the same time (source control in FM forces the whole model to be checked out and cannot check out invidual items within models - hence it was considered too risky/limited to have everything lumped into one big model). It also has the advantage of us being able to re-use components i.e. link them into a new datamart as and when required.

In a segmented modelling approach - you need to be able to join between the end 'reporting' objects ie. between regular/measure dimensions. Otherwise, each time a new datamart is created you would need to re-create the measure/regular dims from scratch (some of our conformed dims are big so this is not feasable).

It would be a backward step to have to re-organise everything into one model.

As for your last point of using a relational model instead of dimensional - we already have a relational model (ReportNet) - one of the main selling points for the Cognos 8 upgrade - is to utlize the so-called new dimensional functionality (e.g. automatic drill-through). Not much point going through the upgrade cycle without this functionality.

Definitely a bug - or something much more serious - a functional design flaw by Cognos.


Regards,

Andy

 

[PaulABC]

You should investigate the Cognos 8 BI Server Updater 8.1.209.78 Hotsite.

The bug fix list includes:

529478 Cross-Join error when viewing level joined between regular and measure dimension.


Perhaps this will address your problem.
Contact cognos for the details.

 

[CognosProfessional]

Thanks Paul! Also, I had an issue with the updater yesterday, but it is no longer a problem. It appears that when you install the updater you should make sure that the task mgr does NOT show these programs running:
BIBusTKServerMain.exe,
cogbootstrapservice.exe,
java.exe,
cogconfigw.exe

Fixed more than just one bug. Also, make sure you install FM mgr and make sure that is running properly and import all your packages first. Apparently, the Server Updater fix does something with what is existing with the FM install. Also, make sure your install is in the Same location as the RN server C8 location. Moving right along...

CP

 

[andygeorge]

Thanks for the reminder Paul - I was the one who actually raised the hotsite...waited a rather long time for it. Will be testing later today to see if it actually works.

CognosProfessional - where did you get that information from ? It doesn't make sense for the updater to touch FM as its a server component fix ie. nothing to do with FM?

Regards,

Andy

 

[CognosProfessional]

Talked with cognos support about it. I thought the same thing. I had to re-install everything to get the services back up.

CP

 

[andygeorge]

yep - this bug is fixed with the updater.

Regards,

Andy

 

[andygeorge]

But.......still does not work if joining between objects from different linked segments. Do Cognos ever test their software - this is absolute crap.

 

[CognosProfessional]

Just make sure you do not create joins between database layers and presentation layers. Do all your joins in one place (namespace).

CP

 

[andygeorge]

The problem isn't to do with joins across namespaces - it is to do with shortcuts. Cognos 8 cannot join between shortcuts (between regular/measure dimensions), and also cannot join regular dimensions that have alternate hierarchies.

 

[cogdev4u]

hi All,

You guys might be able to help me with this issue as you seems to have tested the same water.
I am getting this error when I run my report.

RQP-DEF-0328

The FOR clause in expression 'Year Prompt'.'Year NBR' must not contain multiple facts.

checked for it on cognos site it says that I need to fix determinants.
I set the determinants in my model and I also ran into issue of cognos not recognising joins.
so as per advice in this thread I put all joins in one layer and in other one just defined scope relation (bet dimention and measures) and its working now. But I still get the same error (RQP-DEF-0328 The FOR clause...).

Has any one seen this issue before and aware of any way out.This is very critical for us as some high priority reports are waiting to be built out of this.

Would appreciate any help,hit,
Thanks and Regards,
cogdev4u