Thursday, December 02, 2010

Limitations / Disadvantages of using Calculated Measures / Calculated Members in SSAS

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In my views, Designing is a process that is driven entirely by impact analysis. However trivial a product / tool / technology feature may be, if it's used without thoroughly analyzing the impact it can have on the overall system / solution that has to be developed, this would mean that you just signed up a guaranteed future roadblock.

Calculated measures / members seem like a very straightforward design feature, and whenever you feel need / shortage of some members / measures, calculated ones seems to be a very easily available option from a development perspective. But there is another side of the same, and these points should be kept in consideration before you make the decision of going with calculated members / measures.

1) Drillthrough does not operate on calculated measures or any other calculations that reference calculated measures / calculated members. This means, for example, if you have created a calculated measure on the cube which the user might opt to use as a part of drillthrough dataset, this means that now you are stuck and you need to find a workaround.

2) Calculated measures cannot be secured using Dimension Security in a straight forward manner, in fact they won't be listed at all in the Dimension tab of the role where we define the Dimension security. Also when security is applied on regular members, and due to the same, if they are not available to calculated members, they would fail i.e. when such measures are browsed in client tools like Excel, the value that would be displayed is an error value like #VALUE.

Based on the above two points, calculated measures / members should be scanned against drillthrough and security requirements, so that a trivial overlook in design doesn't translate into a showstopper issue over the period of time at a later stage.

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