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Tuesday, September 1, 2009

Calculated Measure, Member or a Query Calculation?

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I posted previously about calculated members, but until recently, I never really understood when to use a calculated measure, a calculated member or a query calculation when building a report. By chance, I had the opportunity to bring this up to an IBM Cognos employee and was delighted to learn the following:
  • Use Calculated Member or Calculated Measure for dimensional reports where the expression is a member or a tuple-based (as opposed to property-based) value expression.
  • Use Calculate Measure if you intend it to behave like measure (or to replace a measure). In this case, the value expression must not depend on the current measure context.
  • Use Calculate Member if you intend it to behave like measure (or to replace a measure). In this case, you must choose a hierarchy. The value expression must not depend on the current context in this hierarchy.
  • Use Set Expression for set expressions. In this case, you must choose a hierarchy. The set expression must contain only members in this hierarchy.
Finally, use Query Calculation in all other cases.